Appendices E - G-utilization Ratio

8/21/2019 Appendices E - G-utilization Ratio

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City of Palo Alto Long Range Facilities Plan for the RWQCP

APPENDIX E - RWQCP CONDITION ASSESSMENT SUMMARY


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APPENDIX G - SEISMIC EVALUATION OF THE PILESSUPPORTING THE INCINERATOR AND OPERATIONS

BUILDINGS TECHNICAL MEMORANDUM


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CITY OF PALO ALTO

REGIONAL WATER QUALITY CONTROL PLANT

FACILITY REPAIR AND RETROFIT PROJECT

SEISMIC EVALUATION OF THE PILES

SUPPORTING THE INCINERATOR AND

OPERATIONS BUILDINGS


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CITY OF PALO ALTO

REGIONAL WATER QUALITY CONTROL PLANTFACILITY REPAIR AND RETROFIT PROJECT

SEISMIC EVALUATION OF THE PILES SUPPORTING

THE INCINERATOR AND OPERATIONS BUILDINGS

TABLE OF CONTENTS

Page No.

1.0 PURPOSE ..................................................................................................................... 12.0 BACKGROUND ........................................................................................................... 1

2.1 Incinerator Building ............................................................................................ 12.2 Operations Building ............................................................................................ 5

3.0 SEISMIC EVALUATION .......................................................................................... 103.1 Seismic Evaluation Criteria .............................................................................. 10

3.2 Material Properties and Strengths ..................................................................... 113.3 Analysis Procedure ........................................................................................... 12

3.3.1 Mathematical Model .......................................................................... 123.3.2 Soil-Pile Interaction Modeling ........................................................... 133.3.3 Load Combinations ............................................................................ 17

4.0 FINDINGS .................................................................................................................. 174.1 Incinerator Building .......................................................................................... 17

4.1.1 Pile Capacity Check ........................................................................... 184.2 Operations Building .......................................................................................... 20

4.2.1 Pile Capacity Check ........................................................................... 214.3 Discussion ......................................................................................................... 21

5.0 RECOMMENDATIONS ............................................................................................ 225.1 Incinerator Building .......................................................................................... 235.2 Operations Building .......................................................................................... 26

6.0 CONCLUSIONS ......................................................................................................... 26

LIST OF APPENDICES

A – PhotographsB – Soil-Pile Interaction Analysis ResultsC E l ti C l l ti


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LIST OF TABLES

Table 1 Seismic Evaluation Parameters ........................................................................ 10Table 2 Material Properties - Piles ................................................................................ 11Table 3 Pile Lateral Spring Stiffness Values ................................................................. 16Table 4 Load Combinations .......................................................................................... 17Table 5 Analysis Results ............................................................................................... 18Table 6 Pile Shear Capacity Check - Incinerator Building ........................................... 20Table 7 Analysis Results ............................................................................................... 20Table 8 Pile Shear Capacity Check - Operations Building ........................................... 21

LIST OF FIGURES

Figure 1 Incinerator Building Floor Plan .......................................................................... 3Figure 2 Incinerator Building Elevations ......................................................................... 4Figure 3 Existing Pile Details ........................................................................................... 6Figure 4 Operations Building Floor Plan .......................................................................... 8

Figure 5 Operations Building Elevations ......................................................................... 9Figure 6 Incinerator Building Finite Element Model ..................................................... 14Figure 7 Operations Building Finite Element Model ..................................................... 15Figure 8 Site Response Spectra (Ground Acceleration versus Building Period) ........... 19Figure 9 Pile Addition to Existing Pilaster Foundation .................................................. 24Figure 10 Pile Addition to Existing Slab Edge ................................................................. 25


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City of Palo Alto

SEISMIC EVALUATION OF THE PILES SUPPORTINGTHE INCINERATOR AND OPERATIONS BUILDINGS

1.0 PURPOSE

The purpose of this report is to present the findings of our seismic evaluation of the existing piles

that support the Incinerator and Operations Buildings located at the Regional Water Quality

Control Plant (RWQCP) for the City of Palo Alto (City), California.

This evaluation was performed to advance the Facility Condition Assessment (FCA) report by

Kennedy/Jenks Consultants (December 19, 2006) that identified deficiencies in the lateral load

capacity of the piles at the Incinerator Building. The previous study was limited to a preliminary

type investigation of the Operations Building. No evaluation of the Incinerator Building was

made. Rather, it was assumed that the Incinerator Building piles lacked lateral capacity since the

Operations Building, which has a lower seismic load, was found to lack lateral pile capacity.

The current evaluation seeks to provide a more complete evaluation for the Incinerator Building

piles and to verify the preliminary findings for the Operations Building. This current evaluation

attempts to capture the building response to seismic loading by modeling the interaction of the

soil and the foundation. Such modeling accounts for the inherent flexibility of the foundation

interaction with the soil and allows for evaluation at generally larger seismic response periods

than response periods developed using the assumption that the foundation is rigidly attached to

the soil, the default approach taken in most evaluations. Larger response periods typically yield

lower seismic load demands.

Additionally, where the results of the evaluation indicate deficiencies in the lateral load resisting

capacity of the piles, recommendations for mitigation are provided.

2.0 BACKGROUND

The following set of drawings was reviewed for as-built information and was used to obtain the

necessary information for the evaluation of the piles:

Structural drawings of the Incinerator Building prepared by Jenks & Adamson Consulting

Sanitary & Civil Engineers, dated June 1969.


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floor of 44 feet. Two interior mezzanine levels at the south side of the building provide access to

equipment. The building also has a partial basement level for access to the bottom of the

incinerators. Photographs of the building are provided in Appendix A.

The roof of the building is constructed with a one-way spanning, cast-in-place concrete slab that

is 7 inches thick and supported by integral cast-in-place concrete joists and beams. The roof

framing is supported down to the foundation by a single line of rectangular concrete columns at

the interior of the building and by concrete pilasters at the perimeter.

The high mezzanine is located 24 feet above the finished floor on the south half of the building

extending across the full length. The floor area of the mezzanine is approximately 2,500 square

feet. The high mezzanine is constructed with a one-way spanning, cast-in-place concrete slab

that varies in thickness from 8 to 10 inches. The slab is supported by a system of integral

concrete joists and beams that are supported by a row of concrete columns that run along the

center of the building and concrete pilasters at the perimeter.

The low mezzanine is located in the southwest corner of the building and has an approximate

height above finished floor of 10 feet. The low mezzanine is relatively small and has a floor area

of 600 square feet. The floor is constructed with an 8-inch thick cast-in-place concrete slab that

is framed with concrete beams. The floor level is supported down to the foundation by concrete

pilasters and 8-inch thick concrete walls.

The perimeter wall of the building is constructed in a non-traditional configuration with large

tapered pilasters that protrude out from the exterior of the building by several feet at the base and

2 feet into the building. Four pilasters are located at the north and south walls, and two are

located at the east and west walls. The corners of the building are constructed with a concrete

column that is rounded to a 4-foot radius at the exterior of the building. The pilasters are

typically 26 inches thick. Concrete walls that are 9 inches thick fill in most of the gaps between

the panels and corners; however, a number of gaps are open and are covered by the building

finish system and associated framing. The exterior walls and open gaps are finished with a

combination of exposed concrete and corrugated steel panels. Refer to Figures 1 and 2 for thefloor plan and elevations of the building as depicted on the record drawings.

The ground floor of the building is constructed with a cast-in-place concrete slab that varies in

thickness from 13 to 14 inches. The slab is framed with concrete grade beams that span in two

directions and are supported on driven piles. The record drawings indicate three different pile


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pa811f2-8510.ai

Figure 1INCINERATOR BUILDING FLOOR PLAN

INCINERATOR AND OPERATIONS BUILDINGS

PILE SEISMIC EVALUATIONCITY OF PALO ALTO


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and are located below columns, pilasters, and grade beams. Figure 3 shows the three different

pile alternatives that were specified on the record drawings.

The basement is partial to the north side of the building and is located directly below the

incinerators and extends down approximately 8 feet below the finished floor level. Concrete

walls that are 15 inches thick form the perimeter of the basement. The floor slab of the basement

is similar to the ground floor level, except that it has a thickness that varies from 16 to 18 inches.

The building houses two incinerators that are supported at the grade level. Each incinerator has

an approximate height of 25 feet and a diameter of 19 feet. The incinerators are fabricated with a

steel exterior shell and with refractory brick at the interior. Each incinerator is mounted to the

building slab at grade level with six pairs of 1.5-inch-diameter anchor bolts. Space for a third

incinerator is provided at the east end of the building. Two elevated steel-framed mezzanines

provide access around both incinerators. The mezzanine is covered with punched metal plank

grating. Seismic evaluation of the incinerators was completed during the ongoing Long Range

Facilities Plan project.

The exterior of the building has heavy air scrubbing equipment located at the northwest side and

solids storage and handling facilities located at the south side.

The lateral load resisting system of the building is comprised of rigid concrete diaphragms at the

roof and elevated floor levels that transfer lateral loads generated in an earthquake in proportion

to the stiffness of the vertical lateral load-resisting elements. The vertical lateral load-resistingelements are comprised of the perimeter concrete walls and perpendicular pilasters that serve as

shear walls, transferring seismic loads between the elevated levels and the foundation. At the

foundation, lateral loads are transmitted from the soil to the building by the piles and their

connections to the ground floor framing. The piles are embedded directly into concrete grade

beams without any distinct pile caps.

2.2 Operations Building

The Operations Building was originally constructed in 1969 and has a square plan with a side

dimension of 63 feet. The building has two stories above grade with a total height of

approximately 24 feet above the finished floor. Around the entire building, the roof extends 5

feet over the second floor and the second floor extends 5 feet over the first floor The perimeter


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Figure 3EXISTING PILE DETAILS




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The roof of the building is constructed with a 24-inch-deep concrete waffle slab that has a

4-inch-thick deck with ribs spaced on a 30-inch grid. The waffle slab spans in two directions andis supported at the interior by 18-inch-square concrete columns and at the perimeter by tapered

concrete pilasters that are 18 inches thick and nearly 8 feet long at the base.

The second floor of the building is constructed with a 9-inch thick concrete slab that spans in two

directions to integral concrete beams that are supported down to the foundation by square

concrete columns at the interior and tapered concrete pilasters at the perimeter of the building.

The perimeter wall of the building is constructed in a non-traditional configuration with large

tapered pilasters that protrude out from the exterior of the building by several feet at the base.

Two pilasters are located along each side of the building away from the corners. The corners of

the building cantilever at each level. The exterior of the building is finished with glazing at the

second floor and a combination of glazing and corrugated steel siding at the first floor. Refer to

Figures 4 and 5 for the floor plan and elevations of the building as depicted on the record

drawings.

The first floor of the building is constructed with a 9-inch thick concrete slab that spans in two

directions to grade beams that are supported by driven concrete piles. The record drawings

indicate three different pile alternatives that include a 12-inch-diameter, steel pipe-encased

concrete pile; a 15-inch-diameter, steel corrugated-encased concrete tapered pile; and a 12-inch-

square precast, prestressed concrete pile. It is not known which pile type was installed. The piles

are grouped in clusters of four below the four interior columns and spaced apart individually below the perimeter pilasters. Figure 3 shows the three different pile alternatives that were

specified on the record drawings.

The lateral load resisting system of the building is comprised of rigid concrete diaphragms at the

roof and elevated floor levels that transfer lateral loads generated in an earthquake in proportion

to the stiffness of the vertical lateral load-resisting elements. The vertical lateral load-resisting

elements are comprised of the perpendicular pilasters at the perimeter of the building, which

serve as shear walls, transferring seismic loads between the elevated levels and the foundation.

At the foundation, lateral loads are transmitted between the building and the soil by the piles and

their connections to the first floor framing. The piles are embedded directly into the concrete

grade beams without any distinct pile caps


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Figure 4OPERATIONS BUILDING FLOOR PLAN




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Figure 5OPERATIONS BUILDING ELEVATIONS




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3.0 SEISMIC EVALUATION

Seismic evaluation of structures follows standards or guides, such as American Society of Civil

Engineers (ASCE) 31-03 “Seismic Evaluation of Existing Buildings” or ASCE 41-06 “Seismic

Rehabilitation of Existing Buildings.” ASCE 31-03 is intended to serve as a guide for the

preliminary seismic evaluation for buildings and structural members, whereas, ASCE 41-06 is a

standard that contains provisions for seismic rehabilitation of existing buildings. However, either

of these standards may be used for the purposes of a seismic evaluation, which is defined as a

process or methodology of evaluating deficiencies in a building. Since ASCE 41-06 is more

current and more comprehensive, it was used for the seismic evaluation of the building piles. The

acceptance criteria for the materials will bebased upon the procedures set forth in ASCE 41-06

and the relevant material standards, such as American Concrete Institute (ACI) 318-08 “Building

Code Requirements for Structural Concrete.”

3.1 Seismic Evaluation Criteria

Two different types of criteria can be used to define the seismic demand for an evaluation,

namely, probabilistic seismic hazard criteria and deterministic seismic hazard criteria. This

evaluation uses a probabilistic approach because it is the standard for building evaluation and

design. A deterministic approach requires a specific seismologic study that is beyond the scope

of this evaluation. Such an approach is highly sensitive to the attenuation relationship used to

estimate ground motion realized at a site.

A probabilistic seismic hazard approach considers all potential earthquake sources that can

significantly contribute to ground shaking at the site. For a given probability of occurrence, there

is an associated ground acceleration. Building codes and seismic evaluation standards

incorporate this approach when establishing seismic demand levels, which are consistent with

the level of ground shaking that has a 10-percent probability of being exceeded in a 50-year time

period. This level of ground shaking may also be regarded as having a return period of 475 years.

Table 1 contains the seismic evaluation parameters that were used to establish the seismic design

criteria associated with the probabilistic seismic hazard for this evaluation.

Table 1 Seismic Evaluation ParametersS i i E l ti f th Pil S ti th I i t


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Table 1 Seismic Evaluation ParametersSeismic Evaluation of the Piles Supporting the Incinerator

and Operations Build ingsCity of Palo Alto

Parameter Value

Ss 1.50g

S1 0.62g

Fa 0.90

Fv 2.40

SDS 0.90gSD1 0.99g

Peak Ground Acceleration 0.46g

3.2 Material Properties and Strengths

As with any structural or seismic evaluation, two of the more important factors to consider are

the material properties and strengths. The properties and strengths of the materials were gathered

from a review of the record drawings for the Incinerator and Operations Buildings. No materialor destructive testing of any kind was employed to assess the actual in-situ strengths and

properties of the materials being evaluated. Where property values were not reported on the

original construction documents, values consistent with the age of construction and the materials

used were assumed. The properties used in the evaluation for the concrete piles are indicated in

Table 2.

Table 2 Material Properties - PilesSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Property Value

Concrete

Compressive Strength, f’c 3,500 psi

Poisson’s Ratio 0.17

Modulus of Elasticity, E 3,150 ksi

Density 150 pcf

Steel Casing


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exposes the bottom side of foundation elements, which are located at least 3 feet below grade.

Employing material testing of the piles would involve a significant effort since the establishment

of material properties based on sampling and testing will require obtaining samples at numerouslocations.

Knowledge of the actual material strength can help establish higher capacities, but could also

result in reduced capacities. Typically constructed elements have higher capacities than those

assumed provided they are not in a deteriorated state. Decisions to employ testing are typically

made after an initial evaluation so as to avoid expending resources on a task that may not provide

any benefit. Further discussion of testing of materials is provided in Section 5.0 of this report.

3.3 Analysis Procedure

The evaluation of the building piles requires a structural analysis to estimate how the seismic load

demands impact the existing pile system. The capacity of the piles to resist horizontal loading is of

primary interest because shearing of the piles is considered to be a catastrophic type of failure

mechanism. Analysis procedures used in the seismic evaluation of buildings are typically of four types,

namely, linear static procedure (LSP), linear dynamic procedure (LDP), nonlinear static procedure (NSP),

and nonlinear dynamic procedure (NDP). The linear and nonlinear procedures differ in the assumptions

used for material behavior. Linear procedures assume that materials are elastic and respond in the same

manner for all load demand levels. Nonlinear procedures, on the other hand, attempt to capture the

varying response of materials when subjected to actions that create strains beyond the elastic limit.

Incorporating nonlinear and/or dynamic aspects into an analysis can increase the predictive accuracy, but

at significant cost in time and effort. Therefore, when appropriate, seismic evaluations are limited to

linear static procedures. Since the buildings in this evaluation are relatively short, dynamic effects are not

anticipated to have any significant contributions to a building’s response during an earthquake. Also, the

primary member capacity that is being evaluated is the shear capacity of the piles. The behavior of a

concrete pile, when loaded in shear is brittle and exhibits little to no nonlinear behavior. It is considered to

be a force-controlled action. Therefore, a linear static procedure was chosen for the analysis of both

buildings.

3.3.1 Mathematical Model

With any analysis procedure, a mathematical model that represents the structure is needed. For buildings,

mathematical models can be as simple as single vertical beam members or as complex as the actual

building itself with all of its members configured in a manner consistent with the structure. Accuracy will

be sacrificed using oversimplified models More refined mathematical models can yield significantly


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The modeling of the lateral support to the buildings, which is provided by the piles, significantly affects

the accuracy of the analysis. Most support conditions for seismic evaluations are assumed to be rigid, i.e.,

no flexibility, and do not account for any soil-pile interaction. To more accurately capture the response ofthe structure, the pile supports were modeled in a way that accounts for the anticipated soil-pile

interaction. This interaction yields somewhat longer building response periods, which can result in lower

seismic demand estimates compared to analyses that do not consider the soil-pile interaction. This

interaction is modeled by considering the connections of the building to the piles as linear spring

supports.

A graphic representation of the finite element model with the supports (piles) is provided on Figures 6

and 7 for the Incinerator and Operations Buildings, respectively.

3.3.2 Soil-Pile Interaction Modeling

As previously indicated, modeling of the soil-pile interaction can provide more accurate analysis results.

This approach dictates that the lateral support provided by the piles be modeled as springs. To incorporate

this behavior into the FEA, properties for these springs were needed. The spring stiffness is dependent

upon the pile size and stiffness, its assumed connection to the structure, and the properties of the soil that

the piles are embedded within. With all these factors considered, a geotechnical analysis was performed

for each building considering two different pile connections to the structure.

The two types of connections considered for the development of the soil-pile interaction properties are the

fixed-head and free-head conditions. The fixed-head condition assumes that the top of the pile remains

rigidly attached to the mat foundation and grade beam structure of the building. The free-head condition

assumes that the pile is free to rotate at the connection to the building. Each condition is significantly

different and results in different soil-pile interaction. Since actual conditions are neither fully rigid nor

fully free to rotate, the analysis solution is bounded by these two extreme conditions.

Since the installed pile type is not definitively known, the soil-pile analysis was carried out assuming that

the 12-inch-square concrete pile was installed. The stiffness of the piles was assumed to be 50 percent of

the full value to account for member cracking during actual load conditions.

The piles were analyzed using LPile, a specialized software package, to estimate the pile deflection, shear

force, and bending moment as a function of depth for piles at the Incinerator and Operations Buildings.

Also, analyses were run for both the fixed-head and free-head pile conditions. The soil was assumed to be

settled down from the bottom of the mat foundation and grade beams. This assumption is considered to

represent the softest condition that is likely to be present based on the available geotechnical data. The

results of the pile analyses are contained in Appendix B.


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Figure 6INCINERATOR BUILDING FINITE ELEMENT MODEL



Linear

SupportSpring (Typ.)


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Figure 7OPERATIONS BUILDING FINITE ELEMENT MODEL



Linear

SupportSpring (Typ.)


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The spring stiffness values used in the FEA of the buildings is indicated in Table 3. These values were

derived from the soil-pile analysis results. Since the analysis results are limited to lateral displacements of

1.0 inch and less, the reduced stiffness was estimated for larger displacements.

Table 3 Pile Lateral Spring Stiffness ValuesSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Pile Head Condit ion Value

Incinerator Bui lding

Fixed 14.4 kip/in.

Free 4.8 kip/in.

Operations Building

Fixed 18.5 kip/in.

Free 7.3 kip/in.

It is important to note that the stiffness of the soil varies with the load applied. Generally, as the

lateral load on a pile increases, the soil stiffness decreases. However, the seismic load path is not

known. Therefore, it will not be known how or if soil stiffness degradation will occur.

Additionally, there are other foundation variables that will impact the building response. All of

these variables are difficult to assess at best. Therefore, it is advantageous to analyze the building

for the upper and lower bound soil properties to determine how sensitive the building response isto changes in assumed soil properties. For the buildings in this evaluation, it was determined that

the sensitivity to soil properties was rather low. The data provided by the geotechnical analysis is

considered to be a lower bounds estimate of the soil properties. At this lower bound estimate, the

building response was found to have a relatively short period. Therefore, it is not likely that the

softening effects of the soil will be substantial enough to allow for a reduced seismic load to the

building. As discussed previously, softer soil will generally increase the building period, which

can reduce the seismic demand.

Each building has concrete basement walls that can potentially work in conjunction with the

piles to resist lateral loads. The passive resistance of near surface soils is considered to be

substantially less intense than that which can be developed for piles The profile of the east and


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Operations Building are similar. Therefore, the contribution of passive resistance at the basement

walls has been neglected in this evaluation.

3.3.3 Load Combinations

The seismic evaluation of the buildings requires use of the ASCE 41-06 load combinations with

a slight increase to the load factor for the dead load. The dead load factor was increased to

account for the relative uncertainty of the incinerator and other permanent equipment weight.

The combinations used in this evaluation are presented in Table 4, where D represents the weight

of the permanent structure and equipment, E represents the seismic loads, and L is for floor liveload. Additionally, these load combinations were applied in both orthogonal directions for each

building.

Table 4 Load CombinationsSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Load Combination Factors

1 0.9D + 1.0E

2 1.2D + 1.0L + 1.0E

4.0 FINDINGS

Three analyses were run for each building. Each analysis considered a different potential pile

connection type, namely, the fixed-head condition, free-head condition, and pinned support. As

discussed previously, the fixed-head and free-head conditions account for the soil-pile interaction

and assume rigid and free connections to the foundation, respectively. The pinned support

assumption is a rigid support that does not include any soil-pile interaction effects. This

condition was modeled as a baseline to compare the softening effects that modeling the soil-pile

interaction yield.

4.1 Incinerator Building

The analysis results of primary interest are the horizontal reactions at the supports. These

reactions are the shear demand on the piles. The results are summarized in Table 5. The analysis

results are presented in Appendix C. Note that the results presented in Appendix C are for an


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Table 5 Analysis ResultsSeismic Evaluation of the Piles Supporting the Incinerator

and Operations Build ingsCity of Palo Alto

Pile Connect ion TypeBuilding Period

(sec) Average PileShear (kips)

Maximum PileShear (kips)

Fixed Head 0.7 56 76

Free Head 1.2 52 69

Pinned Support 0.2 to 0.3 56 76

Based on the analysis results, the building periods for the fixed-head and free-head conditions

are clearly longer than those estimated assuming the pile connections are pinned supports, which

does not consider any soil-pile interaction. Unfortunately, the increased periods are not

substantial enough to achieve any significant reduction in the seismic load. Figure 8 is a response

spectra for the buildings, which is simply a graph that shows the building acceleration,

equivalent to the seismic load, in percent gravity as a function of the building period. Building

periods greater than 1.10 seconds will generally realize a reduced seismic load because it isoffset from the general earthquake period. If the pile connections are free to rotate, the building

period is about 1.2 seconds and allows for a reduction in seismic load of about 7 percent. Since

this reduction is small compared to the large pile shear forces, the results for the fixed head are

used.

The total weight of the building is estimated to be 9,400 kips. The estimated seismic horizontal

force for the entire building is 8,460 kips. No system reduction factors were considered, sinceloading of the piles in shear is the primary means to transfer lateral load between the soil and the

building.

4.1.1 Pile Capacity Check

Since the pile type that is installed is not known, all three alternatives indicated on the record

drawings were checked against the seismic pile shear demand that was estimated in the analysis.The pile shear capacities were estimated in accordance with the provisions set forth in ACI 318-

08. In estimating the pile shear capacity, 50 percent of the average axial compression load, which

includes seismic loads, was considered. The results are presented in Table 6.

Th il h i l l d i i d i f (Phi f ) l


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1.00

1.20

1.40

1.60

0.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

0.20

0.40

0.60

.

Sa (g) vs. T (sec)

T (sec)

Sa (g)


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Table 6 Pile Shear Capacity Check - Incinerator BuildingSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Pile TypePile Shear

Demand (kips)Pile Shear

Capacity (kips)Demand-Capacity

Ratio

12-inch-squareprestressed concrete

56 33 1.7

15-inch-diameterconcrete

56 33 1.7

12-inch-diametersteel-encased concrete

56 24 2.3

Also, very little research has been done to more accurately assess the shear capacity of steel-

encased concrete piles.

The check of the piles suggests that the demand-capacity ratio (DCR) can be as high as 2.3,

which is a clear indication that the piles lack the needed shear strength to resist the seismic

loading. At this deficiency level, the piles are anticipated to shear off.

4.2 Operations Building

The analysis results of primary interest are the horizontal reactions at the supports. These

reactions are the shear demand on the piles. The results are summarized in Table 7. The analysis

results are presented in Appendix C. Note that the results presented in Appendix C are for an

event with a 2-percent probability of exceedance in a 50-year time period. This evaluation is for

an event with a 10-percent probability of exceedance in 50-years. Therefore, the results in Table

7 have been reduced by a factor of 1.5.

Table 7 Analysis ResultsSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Pile Connect ion TypeBuilding Period

(sec) Average PileShear (kips)

Maximum PileShear (kips)

Fixed Head 0.6 55 59

Free Head 0.9 55 57

Pinned S pport 0 2 55 61


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The total weight of the building is estimated to be 3,068 kips. The estimated seismic horizontal

force for the entire building is 2,760 kips. No system reduction forces were considered, since

loading of the piles in shear is the primary means to transfer lateral load between the soil and the building.

4.2.1 Pile Capacity Check

Since the pile type that is installed is not known, all three alternatives indicated on the record

drawings were checked against the seismic pile shear demand that was estimated in the analysis.

The pile shear capacities were estimated in accordance with the provisions set forth in ACI 318-

08. In estimating the pile shear capacity, 50 percent of the average axial compression load, which

includes seismic loads, was considered. The results are presented in Table 8.

Table 8 Pile Shear Capacity Check - Operations BuildingSeismic Evaluation of the Piles Supporting the Incineratorand Operations Build ingsCity of Palo Alto

Pile TypePile Shear

Demand (kips)Pile Shear

Capacity (kips)Demand-Capacity

Ratio

12-inch-squareprestressed concrete

55 37 1.5

15-inch-diameter concrete 55 36 1.5

12-inch-diametersteel-encased concrete

55 27 2.0

The pile shear capacity was calculated assuming a capacity reduction factor (Phi-factor) equal to

unity. This check is considered to be a force-controlled action and no ductility or redundancy

was considered in the evaluation. The shear capacity of the steel-encased concrete was assumed

to be limited to the lower of the strength of the steel casing or the concrete. The steel is relatively

thin (less than 1/4-inch) and the condition is not known. Also, very little research has been done

to more accurately assess the shear capacity of steel-encased concrete piles.

The check of the piles suggests that the DCR can be as high as 2.0, which is a clear indication

that the piles lack the needed shear strength to resist the seismic loading. At this deficiency level,

the piles are anticipated to shear off.


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Lateral displacement of the building can be significant with excessive collateral and structural

damage. Rotation of the building in plan is also possible.

If the piles had sufficient strength to resist the calculated demands, building lateral deflections

would be significant, being on the order of several inches. At these deflection levels, damage to

connecting piping and other utilities should be anticipated. Additionally, the building may

experience permanent displacement and significant foundation damage.

The results obtained assume that the soil is capable of delivering the large seismic forces that

were estimated in this evaluation. Also, the buildings were not analyzed to evaluate overturning

effects that might include uplift on piles, compression on the piles, and vertical rotation of the

building. Such effects can lead to significant structural and collateral damage. For this

evaluation, net uplift was not identified in any of the analysis results. Furthermore, ASCE 31-03

allows for significant reduction in the calculated overturning actions at the foundation when

evaluating the foundation members.

5.0 RECOMMENDATIONS

Based on the results of the evaluation, it is clear that the existing pile systems for both buildings

lack sufficient shear capacity to resist anticipated seismic loads from an earthquake having a

return period of 475 years. Failure of the pile system can lead to unpredictable behavior and

movement of the building. The foundation can be rehabilitated to provide the necessary shear

capacity to prevent such behavior. Federal Emergency Management Agency (FEMA) 547

“Techniques for the Seismic Rehabilitation of Existing Buildings” contains seismic retrofit

techniques and strategies for the vast majority of building vulnerabilities, including foundation

deficiencies. The cost of foundation rehabilitation is relatively high and disruptive. Therefore,

the consequences of foundation failure should be carefully evaluated to determine whether large

movements are unacceptable. The cost to repair damaged utilities and connections to the building

should be considered. If the foundation system were rehabilitated to resist the seismic shear

demands, displacement will still be relatively large and may still impose failures upon the building connections and utilities.

The basic vulnerability identified with the foundation is the lack of pile shear capacity. The

following strategies and variations thereof are available to address this type of deficiency:


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to the existing piles. A new pile system that is excessively stiff compared to the existing

piles may underutilize the existing pile system.

Removal of a significant amount of mass from the building to reduce the seismic load

demand. Reduction of mass will directly reduce the potential seismic load transferred to

the foundation. The high seismic base shears calculated in this evaluation will practically

eliminate this strategy as a viable alternative.

Although obvious, building replacement could be a viable alternative. If the cost to seismically

retrofit an older building is a substantial percent of the building replacement value, it may beeconomically advantageous to decommission the facility and replace it with a more efficient

system and structure. The building is already more than 40 years old and will require increased

maintenance in the future as the building continues age.

5.1 Incinerator Building

Addition of new concrete piles to supplement the existing foundation is recommended to prevent

shear failure of the existing pile system. Piles can be added around the perimeter of the building

and connected to a new extension of the foundation. It is estimated that a minimum addition of

forty 18-inch-diameter concrete piles will be required to achieve the necessary shear strength.

More piles may need to be added to address bending capacity limitations of the existing pile

system. The existing piles are 12 to 15 inches in diameter. Addition of any new piles will require

a minimum spacing of 4.5 feet from new and existing piles. The spacing of the existing piles

around the perimeter of the building is approximately 6 to 11 feet on center. Based on theexisting spacing, it appears that the addition of new piles around the perimeter is feasible. Piles

can also be added at the interior of the building; however, this will require large equipment

access, which might be limited by the size of the roll-up doors. A conceptual depiction of the

addition of new piles is shown on Figures 9 and 10 for pile additions made at the existing fins

and perimeter slab, respectively.

The existing conditions around the perimeter of the building will impose restrictions ornecessitate additional work so that piles can be successfully installed. The ash system, sludge

storage tanks, and chemical storage along the north and south sides of the building will limit

accessibility and complicate construction.


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New Pile Cap

Extension asrequired

New Piles, Typ 4

at each existingpilaster


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New Pile Cap

Extension as

required

New Piles, atSlab Edge


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Removal of mass can reduce the seismic load to the foundation. However, to make any

meaningful difference for the Incinerator Building, the mass would need to be able to be reduced

by approximately 60 percent. The weight of the ground floor alone exceeds the weight that

would not overload the piles in shear. Therefore, it is not practical to reduce the building weight

alone. To do so would require complete demolition of the building and foundation. A

combination of mass reduction with pile addition can help reduce the total number of

supplemental piles required.

5.2 Operations BuildingAddition of new concrete piles to supplement the existing pile foundation is recommended to

mitigate the identified vulnerability. It is estimated that a minimum addition of twelve 18-inch-

diameter concrete piles will be required to achieve the necessary shear strength. Additional piles

may need to be provided to address bending capacity limitations of the existing pile system. The

existing piles around the perimeter of the building are located below the existing fin walls. Based

on the existing locations, it appears that the addition of new piles around the perimeter isfeasible. Addition of piles at the interior plan of the building does not appear feasible since

access of heavy construction equipment is not practical. A conceptual depiction of the addition

of new piles will be similar to that shown on Figure 9.

The building is completely surrounded at the exterior by a shallow landscaping pond. Installation

of new piles will require the pond to be drained. Repairs to the pond system will likely be

required after any construction work.

Mass reduction of the building would necessitate demolition of the elevated levels and

reconstruction if this strategy were to be employed alone. Given the size of the building, mass

reduction does not appear to be a practical strategy to implement.

6.0 CONCLUSIONS

The seismic evaluation of the existing pile foundations for the Incinerator and Operations

Buildings reveals that the existing piles lack adequate shear capacity to safely resist the seismic

loads imparted by an earthquake with a level of ground shaking that has a 10-percent probability

of being exceeded in a 50-year time frame. Under this scenario, the piles are anticipated to shear


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building. If such behavior is determined to be unacceptable, rehabilitation of the existing

foundation can be achieved by adding new concrete piles with associated pile cap extensions

around the perimeter of each building. A rough order of magnitude cost for construction isestimated to be $1.1 million for both buildings. This estimate assumes that the building is

rehabilitated to meet the life safety performance level that is consistent with the design of new

buildings. Construction will involve mobilization, excavation around the buildings, installation

of additional piles, casting of pile caps, backfilling, repairing/restoring existing construction, etc.

A foundation rehabilitation design will require preparation of engineering plans and perhaps

additional investigation into the existing soils below each building. It should be emphasized thata rehabilitated foundation with adequate shear capacity may still result in relatively large lateral

displacements. Soil improvement may be a necessary part of a foundation rehabilitation design to

help reduce lateral displacements that may be deemed intolerable. The rough cost of soil

improvement techniques, such as injection grouting, has not been considered in this evaluation.

The building replacement cost for each building should be considered before embarking on a

rehabilitation program, as it may be economically advantageous to replace the existing buildings

with new construction that will have considerably longer service lives.


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City of Palo Alto

APPENDIX A - PHOTOGRAPHS


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Figure A-1

Incinerator Bldg: The east elevation. The walls of the building are constructed with steel-framed wall

panels and cast-in-place concrete.


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Figure A-3

Incinerator Bldg: The west elevation.


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Figure A-5

Incinerator Bldg: View of the roof looking from the west to the east. The roof is framed with a concrete slab

and beam system.


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Figure A-7

Incinerator Bldg: Entrance stair to the basement where access to the bottom of the furnaces is provided.


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Figure A-9

Incinerator Bldg: Solids dewatering equipment located at the high mezzanine level that occurs on the

south side of the interior of the building.


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Figure A-11

Incinerator Bldg: View of the concrete columns that support the roof level and high mezzanine down to

the foundation.


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Figure A-13

Incinerator Bldg: Interior of the building at ground level just north of the furnaces.


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Figure A-15

Operations Bldg: Northeast elevation. The exterior of the building is framed with steel-framed siding

panels and cast-in-place concrete cladding and fin walls.


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Figure A-17

Operations Bldg: Southwest elevation.


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Figure A-19

Operations Bldg: Corner of the building with concrete cladding. The floors are framed with a cast-in-place

concrete waffle slab system.


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City of Palo Alto

APPENDIX B - SOIL-PILE INTERACTION ANALYSIS RESULTS

Jan 13, 2011, ground settled from pile cap


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figure titles_run01132011.docx 1 of 1 1/17/11, 8:07 AM

LPILE Results where ground has settled away from bottom of pile caps

Fi gur e 5a - Case 2B0 - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fr ee Head, Load vs Top Def l ect i on

Fi gur e 5b - Case 2B0 - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Def l ect i on vs Dept h

Fi gur e 5c - Case 2B0 - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fr ee Head, Shear vs Dept h

Fi gur e 5d - Case 2B0 - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fr ee Head, Moment vs Dept h

Fi gur e 5e - Case 2B0 - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Soi l React i on

Fi gur e 9a - Case 4D0 - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Load vs Top Def l ect i on

Fi gur e 9b - Case 4D0 - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Def l ect i on vs Dept h

Fi gur e 9c - Case 4D0 - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Shear vs Dept h

Fi gur e 9d - Case 4D0 - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fr ee Head, Moment vs Dept h

Fi gur e 9e - Case 4D0 - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Free Head, Soi l React i on

Fi gur e 13a - Case 2B0x - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Load vs Top

Def l ect i on

Fi gur e 13b - Case 2B0x - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Def l ect i on vs Dept h

Fi gur e 13c - Case 2B0x - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Shear vs Dept h

Fi gur e 13d - Case 2B0x - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Moment vs Dept h

Fi gur e 13e - Case 2B0x - Oper Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Soi l React i on

Fi gur e 17a - Case 4D0x - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Load vs Top

Def l ect i on

Fi gur e 17b - Case 4D0x - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Def l ect i on vs Dept h

Fi gur e 17c - Case 4D0x - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Shear vs Dept h

Fi gur e 17d - Case 4D0x - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Moment vs Dept h

Fi gur e 17e - Case 4D0x - I nci Bl dg, Sof t Gr ound, 12i n SQ Pi l e, 50% Gr oss EI , Fi xed Head, Soi l React i on


2


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L a t e r a l L o a d

( k i p s )

1

2

3

4

5

6

7

8

9

1 0

1 1

1 2



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Lateral Deflection (in)

D e p t h

( f t )

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0

5

1

0

1 5

2 0

2 5

3 0

3 5

4 0



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Shear Force (kips)

D e p t h

( f t )

-8 -6 -4 -2 0 2 4 6 8 10 0

5

1

0

1 5

2 0

2 5

3 0

3 5

4 0



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Bending Moment (in-kips)

D e p t h

( f t )

-100 -50 0 50 100 150 200 250 300 350 400 450 500 0

5

1

0

1 5

2 0

2 5

3 0

3 5

4 0


M bili d S il R ti (lb /i )


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Mobilized Soil Reaction (lbs/in)

D e p t h

( f t )

-300 -250 -200 -150 -100 -50 0 50 100 150 200 0

5

1

0

1 5

2 0

2 5

3 0

3 5

4 0


8


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( k i p s )

. 5

1

1 .

5

2

2 .

5

3

3 .

5

4

4 .

5

5

5 .

5

6

6 .

5

7

7 .

5




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D e p t h

( f t )

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0


Shear Force (kips)


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Shear Force (kips)

D e p t h

( f t )

-8 -6 -4 -2 0 2 4 6 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0




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Bending Moment (in kips)

D e p t h

( f t )

-100 -50 0 50 100 150 200 250 300 350 400 450 500 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0




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( )

D e p t h

( f t )

-400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0


2 6


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( k i p s )

2

4

6

8

1 0

1 2

1 4

1 6

1 8

2 0

2 2

2 4




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D e p t h

( f t )

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0


Shear Force (kips)


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D e p t h

( f t )

-10 -5 0 5 10 15 20 25 30 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0




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D e p t h

( f t )

-1200 -1000 -800 -600 -400 -200 0 200 400 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0




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D e p t h

( f t )

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0


1 9


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( k i p s )

2

3

4

5

6

7

8

9

1 0

1 1

1 2

1 3

1 4

1 5

1 6

1 7

1 8




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D e p t h

( f t )

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0


Shear Force (kips)


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D e p t h

( f t )

-8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0




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D e p t h

( f t )

-1200 -1000 -800 -600 -400 -200 0 200 400 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0



500 450 400 350 300 250 200 150 100 50 0 50 100 150 200


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D e p t h

( f t )

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

City of Palo Alto

APPENDIX C EVALUATION CALCULATIONS


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APPENDIX C - EVALUATION CALCULATIONS


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APPENDIX F – INCINERATORS – SEISMIC EVALUATION

TECHNICAL MEMORANDUM


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CITY OF PALO ALTO

LONG RANGE FACILITIES PLAN FOR THE

RWQCP

TECHNICAL MEMORANDUMINCINERATORS – SEISMIC EVALUATION

DRAFT

City of Palo Alto

LONG RANGE FACILITIES PLAN FOR THE RWQCP

TECHNICAL MEMORANDUMINCINERATORS – SEISMIC EVALUATION


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TABLE OF CONTENTS

Page No.

1.0 INTRODUCTION AND SUMMARY ........................................................................ 1

2.0 BACKGROUND ......................................................................................................... 2

2.1 Existing Facilities............................................................................................. 22.2 Operations ........................................................................................................ 3

3.0 SEISMIC EVALUATION ........................................................................................... 3

3.1 Seismic Evaluation Criteria ............................................................................. 33.2 Historic Seismicity ........................................................................................... 8

3.3 Procedures ........................................................................................................ 8

4.0 CONCLUSIONS........................................................................................................ 22

LIST OF APPENDICES

A – Incinerator PhotographsB – Incinerator Seismic Stability Evaluation

LIST OF TABLES

Table 1 Faults Near City of Palo Alto ............................................................................. 6

Table 2 Seismic Evaluation Parameters per ASCE 7-05 ................................................ 7Table 3 Material Properties – Steel and Concrete ......................................................... 10

Table 4 Material Properties – Refractory Brick ............................................................ 11

Table 5 Hearth Analysis Temperatures ......................................................................... 14Table 6 Hearth Gravity Loads ....................................................................................... 14

Table 7 Hearth Loads and Load Combinations ............................................................. 15

Table 8 Normal Radial Stresses S 21

LIST OF FIGURES

Figure 1 Cross-sectional View of the Incinerator ............................................................. 4

Figure 2 Detailed Section of a Typical Elevated Hearth .................................................. 5

Figure 3 Map of the Peak Ground Acceleration for The 1989 Loma Prieta Earthquake.Courtesy Of The California Geological Survey ................................................. 9

Figure 4 The Finite Element Model of the Incinerator for the Anchorage Evaluation .. 11


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Figure 5 The Finite Element Model Developed for the Evaluation of the Hearths ........ 13

Figure 6 Depiction of Stresses Reported in the Finite Element Analysis ....................... 16Figure 7 Radial and Circumferential Stresses for Load Combination No. 1 (LC100) ... 17

Figure 8 Radial and Circumferential Stresses for Load Combination No. 2 (LC200) ... 18

Figure 9 Radial and Circumferential Stresses for Load Combination No. 3 (LC300). .. 19

Figure 10 Radial and Circumferential Stresses for Load Combination No. 5 (LC500) ... 20

Technical Memorandum

INCINERATORS – SEISMIC EVALUATION

1.0 INTRODUCTION AND SUMMARY

The City of Palo Alto (City) operates two multi-hearth furnaces (MHFs) to incinerate solids at


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The City of Palo Alto (City) operates two multi hearth furnaces (MHFs) to incinerate solids at

the Regional Water Quality Control Plant (RWQCP). The incinerators were originally fabricated

in 1971 and began operation in 1972 and are located within the Incinerator Building, which is a

concrete-framed building with a concrete steel-framed roof. The plant is located within a region

that is well known for its potential for large earthquakes. Therefore, buildings and large

equipment may, at any time, be subjected to strong ground motions without warning. As part of

the Long Range Facilities Plan (LRFP), the City requested Carollo Engineers, Inc. (Carollo) to

provide a description of the MHFs, an overview of the approach and procedures used, and

recommendations for addressing potential deficiencies identified.

Over the years, the design of buildings and non-building structures has improved considerably

with the advancement of knowledge within the fields of structural engineering and seismology.

As a result, structures designed and constructed within the last 20 to 30 years may be expected to

perform better than those constructed in an earlier time period. Furthermore, design standards

and guides for special structures, such as steel tanks and silos, have also evolved over the years

to include necessary seismic design provisions. The incinerators are considered to be a special

type of structure that is quite different than a typical tank due to the internal operations, materials

of construction, and the service conditions to which the structure will be subjected. As a result,

one would expect that a specific standard exists to address structural concerns, especially relatedto seismic design. However, due to the fact that solids incineration using MHFs has been

superceded by other technologies, such a standard did not develop. Additionally, the MHFs are

more than 40 years old. Consequently, given the age of the MHFs and lack of a design standard,

there is a need to more clearly understand what the seismic-related risks might be to both the life

safety of plant operators and to the operation of the solids handling process. Carollo was scoped

to evaluate the MHFs to identify potential seismic-related deficiencies of the structural

components.

The seismic evaluation of the incinerators included a visit to the site on November 3, 2010, a

2.0 BACKGROUND

2.1 Existing Facilities

The two incinerators are located within the Incinerator Building and are approximately 25 feet inheight and nearly 19 feet in diameter. Furnace No.1 and Furnace No. 2 (the incinerators) are

situated along the north side of the building, with Furnace No. 1 closest to the west side of the


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g g,

building. The incinerators are constructed with an exterior steel shell that is 3/8-inch thick. The

shell is circumferentially spliced together with three bolted, steel plate sections that are of equal

length. The interior of each incinerator is comprised of six hearths. Each hearth is constructed

with a low-profile sprung arch of refractory brick material that relies upon the compressive

pressure between each brick to maintain stability against collapse. The supporting compressive

pressure between each brick is comprised of two components, namely, the weight of the bricks

and the interlocking pressure created by carefully fitting the bricks together during construction,

the latter pressure being difficult to estimate. The interior perimeter is constructed with a single

4.5-inch wide layer of refractory brick and a 9-inch thick layer of castable refractory material for

insulation, creating a total insulation thickness of 13.5 inches. This insulation also serves to

vertically support all of the hearth levels. The exterior shell is reinforced with an additional5/8-inch by 6-inch tall steel plate at each hearth level to provide the necessary resistance to the

thrust loading generated by the arch action of the hearth and the thermal expansion caused by

heating within. The reinforcing rings are spliced with bolts. The top and bottom of the

incinerators are framed with steel framing that is insulated with castable refractory.

A mechanical shaft is located at the center of the incinerator. The central shaft is fitted with

rabble arms at each hearth level to move the solids through the incinerator. The shaft is insulatedwith castable refractory. The hearth levels have alternating openings to allow the passage of

solids from the top to the bottom. The openings alternate from the center to the perimeter at each

subsequent hearth.

Each incinerator is mounted to the building slab at grade level with six pairs of 1.5-inch diameter

anchor bolts. For access to equipment, an 8-foot deep pit is located below the bottom of the

incinerators. Additional concrete piers provide support to the center drive mechanism andmechanical equipment. The foundation of the building is comprised of concrete piles that extend

down into the site soils.

2.2 Operations

The plant currently operates the incinerators on an annual alternating cycle where one is online

for a year while the other is off-line for maintenance and repair. At the time of the site visit in

November of 2010, Furnace No. 1 was in operation. Solids are introduced into the incinerator atthe top on a conveyor belt after passing through a belt-press filter. The solids are heated at

different temperatures at each hearth level to induce drying and combustion. The rabble arms


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different temperatures at each hearth level to induce drying and combustion. The rabble arms

constantly spread and move the solids across the hearth surface. Ash is collected at the bottom

hearth and extracted. The maximum normal operating temperature was reported by plant staff to

be approximately 1,500 degrees Fahrenheit, with spikes occasionally reaching 2,000 degrees

Fahrenheit. Heating is achieved by burning natural gas at select hearth levels.

Start-up and shutdown of the incinerator is performed over multiple days to avoid spalling from

boiling water and to avoid thermal shock to the interior materials, which can cause differential

expansion/contraction that can potentially destabilize the refractory brick resulting in a hearth

collapse. The refractory brick does not have the capacity to resist tensile forces since there is no

physical bond or connection between the individual bricks. This is understood to be an inherent

risk of operating a MHF. During heating the hearths expand, but are restrained by the exterior

steel shell, which causes the hearth to displace vertically at the center.

Excerpts from the record drawings of the incinerators are provided on Figures 1 and 2.

Photographs of the incinerators are contained in Appendix A.

3.0 SEISMIC EVALUATION

Seismic evaluation of structures typically follows a standard or guide, such as American Societyof Civil Engineers (ASCE) 31, “Seismic Evaluation of Existing Buildings.” Non-building

structures may have a specific design standard that can be used as a guide, such as American

Water Works Association (AWWA) D100 for prestressed concrete tanks. However, for the

incinerators, no such standard exists. Therefore, the seismic hazard used in the assessment and

the acceptance criteria for the materials will be based upon the principles contained in ASCE 7-

05, “Minimum Design Loads for Buildings and Other Structures,” and the relevant current

material standards, respectively.

3.1 Seismic Evaluation Criteria


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Figure 2 Detailed Section of a Typical Elevated Hearth

California is in a region of the world that has experienced significant seismic events and is

therefore an area of high seismic risk. The primary source of California’s seismicity is derived

from its location, which straddles the North American and Pacific Plates, which are moving in

opposite longitudinal directions. The primary interface between the two plates is the San Andreas

Fault. The plate interactions also have created a host of complementary earthquake faults that

generally are parallel to the San Andreas Fault. Examples of these faults include the Newport-

Inglewood Fault in Southern California, the Hayward Fault in the Bay Area, and the Garlock

Fault in the Owens Valley.

Some significant historic damaging earthquakes include the 1857 Fort Tejon earthquake on the

San Andreas Fault, the 1906 Great San Francisco earthquake, the 1971 San Fernando earthquake,

the 1989 Loma Prieta earthquake, and the 1994 Northridge earthquake.

Some substantial faults that may influence the RWQCP site are indicated in Table 1. These faults

are those that are known to have been active within the last 11,000 years. Note that this list is not

meant to be comprehensive. Bear in mind that earthquakes are not confined to known or listed

faults. Seismologists are still actively identifying and cataloging new faults that were previously

unknown. The thrust fault that generated the 1994 Northridge earthquake was one such fault.

Two different types of criteria can be used to define the seismic demand for an evaluation,

Table 1 Faults Near City of Palo Alto (1)

Fault Name Distance from RWQCP Site (miles)

Monte Vista-Shannon 6.0

San Andreas 8.0

Hayward-Rodgers Creek 11.0

Calaveras 15 0


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Calaveras 15.0

San Gregorio 18.0

Sargent 24.0

Greenville 29.0

3.1.1 Probabilistic Criteria

A probabilistic seismic hazard approach considers all potential earthquake sources that can

significantly contribute to ground shaking at the site. For a given probability of occurrence, there

is an associated ground acceleration. Building codes and seismic evaluation standards

incorporate this approach when establishing seismic demand levels, which are consistent with

the level of ground shaking that has a 10-percent probability of being exceeded in a 50-year time period. This level of ground shaking may also be regarded as having a return period of 475 years.

Table 2 contains the seismic evaluation parameters obtained from ASCE 7-05.These parameters

were used to establish the seismic design criteria associated with the probabilistic seismic hazard

for this evaluation.

3.1.2 Deterministic Criteria

A deterministic approach is not used in this evaluation as it is beyond the scope of work.

Development of a deterministic approach requires a specific geologic and seismologic study. A

deterministic approach considers an earthquake of a particular magnitude that might occur along

a particular segment of a fault at a specified distance from the site. The particular earthquake

considered in a deterministic approach may be considered as the maximum credible event or an

event that has a greater potential to occur. Such an approach is often more suited for qualitativeevaluations, such as emergency response studies, or worst-case scenarios, as such events are less

likely to occur in any given time period and can result in significantly higher level forces for an

evaluation

Table 2 Seismic Evaluat ion Parameters per ASCE 7-05

Parameter Value

Soil Site Class E

Latitude 37º 27’ 11’’

Longitude -122º 6’ 40’’

Ss 1.50g


118/169

Ss 1.50g

S1 0.62g

Fa 0.90

Fv 2.40

SDS 0.90g

SD1 0.99g

Peak Ground Acceleration 0.46g

Notes:

(1) g = vertical acceleration due to gravity at the Earth's surface

(2) Ss = mapped maximum credible earthquake, 5 percent damped, spectral response

acceleration parameter at short periods(3) S1 = mapped maximum credible earthquake, 5 percent damped, spectral response

acceleration parameter at 1 second

(4) Fa = short-period site coefficient

(5) Fv = long-period site coefficient

(6) SDS = design, 5 percent damped, spectral response acceleration parameter at shortperiods

(7) SD1 = design, 5 percent damped, spectral response acceleration parameter at 1 second

A previous geotechnical report prepared for an incinerator rehabilitation project at the RWQCP

in 1998 by CH2M Hill contains a

Appendices E - G-utilization Ratio

Documents

Transcript of Appendices E - G-utilization Ratio