Performance of Precast and Prestressed Concrete in Mexico ... · crete manufacture a variety of...

Special Report

Performance of Precastand Prestressed Concrete

in Mexico EarthquakeMark FintelConsulting EngineerChicago, Illinois

Note: This report is based upon the author's observa-tions during a visit to Mexico, October 13-17, 1985, onbehalf of the Prestressed Concrete Institute.

The extreme severity of the earthquakeand major aftershock that hit the west

coast of Mexico, September 19 and 20, 1985,caused the collapse of several hundred mul-tistory buildings in Mexico City [about 400km (250 miles) away from the epicenter].An estimated 10,000 people lost their livesand countless more were injured. In addi-tion, a quarter million people lost theirhomes.

Most of the collapses were reinforcedconcrete framed buildings in the range ofsix to fifteen stories. Five of the collapsedbuildings contained precast concrete com-ponents as part of their structural systems.Many buildings and parking garages inMexico City utilizing precast concrete ele-

ments withstood the earthquake withoutdistress.

In Lazaro Cardenas [about 30 km (19 miles)from the epicenter], large fully precastbuildings in the fertilizer plant resisted theearthquake exceptionally well. Also,throughout the country and within the cit-ies, the concrete bridges withstood theearthquake without damage.

This report presents the author's obser-vations of the performance of precast andprestressed concrete during his visits toMexico City and Ldzaro Cardenas. How-ever, prior to getting into this discussion, itis necessary to describe the unique seis-mological aspects of the earthquake and theresulting overall damage.

18

Reports on the performance of precast and pre-stressed concrete structures (most of which werecomposite) in Mexico during the earthquake ofSeptember 19, 1985, and the severe aftershockthat struck on the subsequent day.

SEISMOLOGICAL ASPECTSThe earthquake that hit Mexico at 7:19

a. m. on September 19, 1985 had the epi-center about 30 km (19 miles) off Mexico'sPacific coast (see map). Within 36 hours, at

7:38 p.m., there was an aftershock emanat-ing from the same general epicentral re-gion. The quakes registered Richtermagnitudes of 8.1 and 7.5, respectively.

In Mexico City, 400 km (250 miles) awayfrom the epicenter, the underlying firm soil

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24 32

TIME, SECONDS

recorded a maximum acceleration of less than4 percent of gravity with predominant longperiods since the short period componentsof an earthquake are usually filtered out atrelatively short distances from the epicen-ter. In sections of the city, located in thehills, the earthquake was only mildly per-ceived. The layers of soft sedimentary ma-terials of the filled in lake bed upon whichmuch of Mexico City is founded, however,amplified the bedrock accelerations verysignificantly.

At the Communications and Transporta-tion Center (SCT Station) in the city, in-struments measured over 20 repetitions ofalmost steady state pulses of between 5 and20 percent of gravity as can he seen in Fig.1. The pulses came at a rate of every 2 sec-onds. Total duration of severe shaking wasabout 60 seconds. Such a long duration ofintense motions has not been experiencedin previously documented earthquakes.

Also, the peak acceleration of this recordwas more than twice that experienced inMexico City's previous most severe earth-quakes. The shape of this record resemblesmore of a response curve than that of a typ-ical accelograph, thus indicating the specificseismic response characteristics of the par-ticular depth and make-up of the lake bedfill.

Fig. 2 shows the spectral accelerationscalculated from the SCT Station accelo-graph. This spectra is compared with the El

Centro (1940) spectra which has become astandard for comparison.

Also shown for comparison are the spec-tra recommended in ATC-3. * As can be seenfrom the graph, accelerations in the periodrange between 1.5 and 3.0 seconds gener-ated by the Mexico City event are consid-erably higher than those generated by otherevents.

The corresponding calculated amplitudeof the soil displacement of the SCT recordis up to ± 20 cm (± 8 in.) from the initialposition.

At another location in the city the accel-eration pulses came every 3¼ seconds (be-cause of a different depth and make-up ofsoft deposits) with a maximum accelerationof about 12 percent of gravity.

The earthquake intensity was assessed onthe Modified Mercalli scale to range be-tween V and IX in the various parts of thecity.

In LAzaro Cardenas, on Mexico's west coastlocated about 30 km (19 miles) from the ep-icenter, the intensity was estimated as IXon the Modified Mercalli scale. The peakaccelerations recorded in the epicentral re-gion were 17 percent of gravity for a dura-tion of 40 seconds with predominantfrequencies in the 0.2-seconds range.

* "Tentative Provisions for the Development of SeismicRegulations for Buildings" by Applied TechnologyCouncil, associated with SEAOC.

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Fig. 2. Elastic response spectra for 5 percent damping. Courtesy ofEnglekirk and Hart Inc., Los Angeles, California.

OVERALL DAMAGEAs a result of these unusually long and

intense earthquake motions, about 180buildings collapsed and 85 were severelydamaged and designated for immediatedemolition in Mexico City.* Most of the se-vere damage was concentrated in severalsections of the city within the filled-in lakebed.

The majority of these 265 (180 + 85)buildings were in the six to fifteen-storyrange. Categorized by structural types: 143of these were concrete frames; 85 flat platesor waffle slabs with or without filler blocks;10 structural steel frames; 17 masonry con-struction; and 10 of other structural types.

Classifying these buildings by their age:• 69 were constructed prior to 1957• 149 between 1957 and 1976• 47 constructed after 1976

* According to a preliminary report issued by the In-stitute of Engineering at the National AutonomousUniversity of Mexico.

This age division corresponds to the dif-ferent code requirements in force at theseparticular time periods (see section onBuilding Codes below).

The most severe losses were in concreteconstruction (228 buildings out of 265) whichis the predominant construction material inMexico. Of these, 52 were built before 1957,133 were built between 1957 and 1976, and43 were constructed since 1976.

It appears that many frame buildings col-lapsed predominantly due to shear failuresof columns resulting from large interstorydistortions with the slabs "pancaking" oneon top of the other (Fig. 3). In some flat slabbuildings the primary failure appeared to bepunching shear in the slabs around the col-umn periphery with the columns protrud-ing several stories high above the pancakedfloors (Fig. 4).

There were numerous instances of a groupof upper slabs collapsing with the remainderof the structure left standing (Fig. 5). Therewere also cases where a group of stories


within the height of the structure collapsedwhile leaving intact several stories above anda number of stories below (Fig. 6).

The disastrous effects in Mexico City re-sulted from resonance between the numer-ous, intense 2-second pulses of theearthquake and buildings having a period ofvibration in the 2-second range.

Frame buildings in the twenty-story range(concrete or steel) entered the earthquakewith a 2-second period and were immedi-ately severely excited by the 2-second pulses.Note that the customary design formula forthe period of a frame building is 0.1 secondper story.

Shorter concrete frame buildings in thesix to fifteen story range (the range wheremost of the collapses occurred) entered theearthquake with natural periods of 0.6 to 1.5seconds. These initially stiffer structuresgradually became more flexible and length-ened their periods due to cracking andyielding in sequential sways until their pe-riod of vibration reached 2 seconds. These

on

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Fig. 3. Pancaked multistory building.

Fig. 4. Columns protruding above pancaked floors failed in punching shear of a flatslab multistory building.

22

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Fig. 5. Collapsed upper stories.

Fig. 6. Collapsed middle stories.


Fig. 7. Building sunk relative to sidewalk.

causing a building to settle as a block byabout a third of its ground story (Fig. 7).

Buildings containing shear walls per-formed generally well, offering a betterdamage control to nonstructural elementsby limiting the drift during the earthquakeresponse.

An important observation is that an over-whelming majority of the buildings locatedin the area of maximum damage, even thosein the period range susceptible to thisearthquake, fared extremely well. In mostcases, collapsed buildings were surroundedby others which went through the earth-quake undamaged (Figs. 8 and 9).

BUILDING CODESBefore 1957, the Mexican Building Code

had no special detailing requirements forseismic design and specified a lateral designforce of 0.025g. After the 1957 earthquake,the lateral force requirements were gradu-ally increased.

In the 1976 Code a higher lateral design

buildings then came into resonance with the2-second pulses causing their collapse.

The extremely long duration of the earth-quake collapsed buildings which could havesurvived a lesser number of earthquakepulses.

Hammering of neighboring buildings notseparated by proper seismic joints causeddamage in many instances. Particularly,where adjacent buildings were of differentheights, the lower building created a but-tressing effect and caused a damaging whip-lash of the protruding part of the tallerneighbor.

While flexible buildings had the tendencyto collapse in a "pancake" manner due tocolumn failures resulting from large inter-story distortions, a case of a very stiff build-ing was observed which developed extremelyhigh overturning moments and tilted overin its entirety, pulling the friction piles fromthe ground.

There were also cases of soil subsidence Fig. 8. Most buildings behaved well.

24

Fig. 9. Most buildings behaved well.

force requirement was specified. The de-tailing requirements introduced in the 1976Code are less stringent than the require-ments of ACI 318-83, Appendix A.

Following the 1985 earthquake, emer-gency regulations were introduced in-creasing considerably the lateral forcerequirements and specifying stricter rulesaimed at increasing the rigidity of buildingsto reduce drift, limiting plan eccentricity toreduce torsion, improve inspection require-ments, and other provisions. These emer-gency regulations will eventually, aftercareful scrutiny, become part of the Mexi-can Code.

PRECAST PRESTRESSEDCONCRETE PRODUCTS

Currently, there are about ten manufac-turers of precast prestressed concrete prod-ucts in Mexico City, two of which produceexclusively architectural precast concrete.

Structural Precast ConcreteThe producers of structural precast con-

crete manufacture a variety of standardcomponents such as single tees, a variety ofdouble tees [2 m, 2.5 m and 3.0 m (6.6, 8.2,and 9.8 ft), hollow-core slabs (Spancrete,Dycore and Spiroll), thin precast pre-stressed plates to be used for composite slabs,small precast beams used with concrete fillerblocks for spans up to 6.1 m (20 ft), all typesof beams for custom designed industrialplants, columns on an individual order ba-sis, mostly up to five stories high (only oc-casionally up to nine stories), standard andspecial bridge girders and other complexshape elements for special projects.

In recent years, precast concrete manu-facturers have been using portable precast-ing plants at the sites of major projects toavoid long distance hauling of large precastelements.

The prestressing industry annually uses


between 7000 and 8000 tons of prestressingwires and another 7000 tons of prestressingstrands.

Only a very small percentage of buildingsin the center of Mexico City utilize struc-tural precast concrete. Most of the precastbuildings are outside the center of the city.Within the city, use of cranes for erectionof large elements is difficult in the narrowstreets with heavy traffic. Several multistoryparking garages have been built with pre-cast elements, some of them in the area ofmaximum damage.

About 40 percent of bridges in the Mex-ico City area are constructed with precastprestressed members using substantialamounts of cast-in-place concrete to tie thebridge components together in order toachieve a behavior similar to that of mono-lithic concrete.

It should be noted that the awareness ofthe engineering community of the seismicproblem has resulted in using precast ele-ments in buildings with cast-in-place con-crete to create composite action. Allstructural slab elements (single tees, doubletees, hollow-core slabs, and small beams withfillers) are used with a cast-in-place rein-forced concrete topping.

The connections between slabs and beamsand beams and columns are cast in placewith the reinforcing bars mostly welded. Inrare cases, post-tensioning is used to createconnections between beams and columns.In the majority of city buildings using pre-cast elements, the columns are cast in place.Only rarely were shear walls used in thesebuildings.

Architectural Precast Concreteand GFRC

There are about 1000 buildings up to fif-teen stories in height in Mexico City cladwith architectural precast concrete panels(Figs. 10 and 11).

Currently, there are about a dozenbuildings in Mexico City in which glass fiberreinforced concrete (GFRC) was used asbacking for the facing concrete in architec-tural precast panels. Two of the buildings

are in the twenty-story range, the remain-der are four to five stories in height. Theperformance record of these GFRC panelsover their 4 to 5 year life is satisfactory.None of these buildings are located in zonesof earthquake damage.

PERFORMANCE OFSTRUCTURES WITH

PRECAST COMPONENTSThis section presents the author's obser-

vations of the performance of structures us-ing precast concrete components in MexicoCity and Ldzaro Cardenas.

Mexico CityBuildings — Throughout Mexico City

there is a significant number of multistoryresidential and commercial buildings andparking garages constructed with precastelements, although they represent only asmall percentage of the buildings in the city.There are also many single-story and two-story schools built with precast elements.

Although the majority of these buildingsare in areas which suffered little damage,many buildings using precast elements arelocated in zones of severe damage. Inspec-tion of many of them in the area of severedamage showed little or no damage. Someof the inspected buildings and parking ga-rages are described in Appendix A.

Five of the 265 collapsed or most se-verely damaged building structures con-tained precast elements.

Inspection of the remains of two of thesecollapses — the six-story Maternity Ward atthe General Hospital (Figs. 12 and 13); andthe partially collapsed seven-story publicparking garage at Carranza Street (Figs. 14and 15) — showed many connections be-tween columns and beams intact. The re-mains and positions of the pancaked slabssuggested that collapses were caused byfailures unrelated to the precast elementsor their connections. Thus, the earthquakeperformance of these buildings was similarto those of monolithic concrete frames.

26

Fig. 10. Architectural precast concrete cladding.

Fig. 11. Architectural precast concrete cladding.

PCI JOURNAUJanuary-February 1986 27

Fig. 12. Remains of six-story Maternity Ward, General Hospital.

Fig. 13. Remains of six-story Maternity Ward, General Hospital.

28

As can be seen in the figures, the Ma-ternity Ward used double tee slabs with 5cm (2 in.) topping, while the parking garageused topped hollow-core slabs. The Mater-nity Ward was a free standing structure andcolumn failures might have been the pri-mary cause of collapse. The parking garagestood in the middle of the block squeezedin between neighboring structures; ham-mering against the adjacent strictures mighthave caused the failure.

The remains of the other three collapsedbuildings using precast components couldnot be inspected since they had been clearedby October 12, 1985.

Bridges — It is worthwhile to mentionthat none of the concrete bridges in MexicoCity, whether cast in place or precast, suf-fered any damage during the earthquake.Also, there were no official reports of bridgefailures from the interior of the country.

Architectural Precast Concrete — Of the Fig. 14. Partially collapsed seven-storymore than 1000 buildings clad with archi- public parking garage at Carranza St.

Fig. 15. Detail showing partially collapsed seven-story parking garage at Carranza St.


PLATE OR ANGLE°

4 MIN.ATTACHED TO STRUCTURE

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Fig. 16. Detail of architectural panel attachment.

Fig. 17. Panel attachment detail.

30

tectural precast concrete panels, many werein the zones of severe damage. The archi-tectural cladding panels performed very wellduring the earthquake (Figs. 10 and 11).

It is customary in Mexico to attach ar-chitectural panels by welding the insert platesat the bottom of the panel to the structureand to use the detail shown in Fig. 16 atthe top of the panels to allow for relativemovements of the panels due to thermal andshrinkage effects of the panels, in additionto shrinkage and creep of the columns. Thisdetail also allows for frame distortions dueto wind or earthquakes without damagingthe precast panels. Fig. 17 shows a pictureof this detail.

There were only two cases of poor per-formance of architectural cladding during theearthquake. In the case of the six-story "Se-guros la Republica," a number of panelspulled away several inches at their upperflexible connections after some bolts shearedoff. The lower welded connection of thepanels remained intact and kept the panelsfrom falling off the building. The originalconnections were re-established after theearthquake by removing the sheared boltsand installing new ones.

The other case was that of the twelve-story building at the corner of Nuevo Leonand Campeche Avenue in which the upperthree, two-story architectural panels fell offthe building during the earthquake. Thosewere U-shaped panels, 1.20 m (4 ft) wideand 25 cm (10 in.) deep, that covered thetwo columns at an expansion joint and wereattached to only one of the two columns topermit the joint to function. Apparently,during the earthquake the joint opened widerthan the space provided, thus throwing offthe panels.

In a number of instances, where signifi-cant nonstructural damage to multistorybuildings attested to interstory distortions,the architectural cladding of these buildingsremained fully intact. This stability indi-cates that the detail shown in Figs. 16 and17, which was used in these buildings, pro-vided sufficient distortion capacity to allowthe distortions of the structure withoutdamage to the panels.

Lazaro CardenasThe seismic performance of a number of

very large, fully precast industrial buildingsin the fertilizer manufacturing plant in L'a-zaro Cardenas, under construction since1978, is of particular interest due to theirproximity to the epicenter of the earthquake[about 30 km (19 miles)] and due to the re-corded strong motions there as describedpreviously.

One of the reasons prestressed concretewas selected for these structures was theneed for protection against corrosion, whichis a usual requirement in the environmentof chemical plants. At this fertilizer plantthere were three giant horizontal industrial"A-frame" silos* (Fig. 18). The fourth isnow under construction. Each of the three-hinged silos measures 68 X 280 in (224 x918 ft) in plan and is 28 m (92 ft) high atits apex.

The silos, described in more detail in Ap-pendix B, consisted of two 44.7 in (146.6 ft)long precast prestressed channel beams tiedtogether by post-tensioned beams under thefloor.

There were also two-story plant build-ings; one three bays and the other two bayswide. The roofs consisted of simply sup-ported, channel section, precast prestressedbeams spanning 25 m (82 ft). See AppendixB for more detailed descriptions of thesebuildings.

At the location of the precast plant build-ings the ground movements were extremelyviolent. In some locations inside and out-side of the buildings fine granular soil wasshooting out during the earthquake likegeysers, creating large mounds up to 1 m(3.3 ft) in height.

Within the two-hay building, the previ-ously level, slab-on-grade became wavy (Fig.19), inducing a difference in elevation of 1m (3.3 ft) between the lowest and highestpoints. The middle row of columns settledrelative to the exterior rows registering

* "Giant Precast Silo for Storing Fertilizers Built inMexican Port," by Jos€ Ma. RiobGo, PCI JOURNAL,V. 27, No. 4, July-August, 1982, pp. 108-119.


Fig. 18. Giant horizontal silo.

measured differentials up to 60 cm (24 in.).There was also extensive damage to theroadway running along the storage buildingwith the roadway settling in some locationsup to 50 cm (20 in.).

Both the giant silos and the plant build-ings performed very well during the earth-quake. Only a very few purlins had fallenoff their supports in the silos. In the twoplant buildings several beams shifted on theirsupports and only two beams (out of 60) ex-hibited slight shear cracking (Fig. 20) in ad-dition to some minor repairable distress anddislocation.

This exemplary performance of the pre-cast elements, despite the large differentialsettlements, was a result of the statically de-terminate structural configuration in whichdifferential settlements do not cause addi-tional moments or shears. This structuralsystem with corresponding details allowingrotations without loss of support contrib-uted to the excellent performance duringthe earthquake.

OBSERVATIONS1. The disastrous earthquake off Mexi-

co's Pacific coast on September 19, 1985 andthe aftershock on September 20, 1985, hav-ing Richter magnitudes of 8.1 and 7.5, re-spectively, caused an amount of destructionin Mexico City, 400 km (250 miles) awayfrom the epicenter, never before experi-enced in the western world in modem times.

2. Accelerations of only 4 percent ofgravity were registered on firm groundaround the city. These were amplified to 20percent of gravity by the soft layers of thefilled-in lake bed. The earthquake was alsoof unusually long duration consisting oftwenty 2-second pulses which caused dis-astrous resonance with structures havingperiods of vibration in the 2-second range.

3. Some 265 multistory buildings, mostof them ranging from six to fifteen stories,collapsed or were severely damaged. Mostcollapses of concrete structures appeared tohave occurred due to large interstory dis-tortions causing shear failures of columns.

32

Fig. 19. Slab waves 1 m (3.3 ft) high.

Fig. 20. Shear crack in roof beam.


4. As in previous earthquakes, buildingscontaining shear walls performed well, of-fering better damage control by limiting drift,and thus also reducing the danger of col-lapse.

5. The choice of a structural system withsufficient overall stiffness cannot be over-emphasized. In concrete structures theoverall rigidity can be provided either byincorporating shear walls or by column andbeam sizes to result in adequate stiffness.Providing for a given seismic intensity, alevel of strength consistent with the degreeof available ductility will ensure survival inan earthquake. However, the best detailingof members and connections cannot com-pensate for an inadequate structural system.

6. There are many buildings and mul-tistory parking garages using precast com-ponents in Mexico City (some in the areasof severe damage) which withstood theearthquake without damage or distress.

7. Five multistory buildings (one park-ing garage among them) using precast com-ponents suffered total or partial collapse.These were composite structures using asubstantial amount of cast-in-place con-crete. Inspection of the debris suggests thatthe reasons for failure of these buildings werethe same as for the concrete frame struc-tures and were not related to the use ofprecast prestressed components.

8. Of the 1000 buildings clad with ar-chitectural precast concrete panels, manywere in the area of the city in which severedamage occurred. In many distressed build-ings, the architectural panels showed nodistress due to the flexibility of their attach-ment details. Only two buildings had somedistress of architectural panels.

9. The twelve buildings ranging from twoto twenty stories clad with GFRC panelswere not in the area of earthquake damage.

10. Forty percent of Mexico City bridgesare built with precast concrete components.None of the bridges (cast in place or precast)suffered any damage.

11. In Ldzaro Cardenas [30 km (19 miles)from the epicenter] a number of fully pre-cast and prestressed large industrial struc-tures performed extremely well during theearthquake despite considerable groundmovements. The four three-hinged giant siloswith beams of 44.7 m (146.6 ft) in lengthlost only a few purlins. In a plant buildingthe simply supported beams spanning 25 m(82 ft) experienced only a few minor shearcracks in two (out of 60) beams despite dif-ferential column settlements of up to 60 cm(2 ft).

In conclusion, it should be emphasizedthat this report presents primarily the au-thor's observations of the performance ofprecast and prestressed concrete structuresin the Mexico Earthquake. Because of timeand financial limitations, it was not possibleto obtain an in-depth technical perspectiveon seismic performance that includes causeand effect relationships. Nevertheless, theauthor believes that the opportunity existsto conduct a comprehensive study of thebehavior of not only the hundreds of failedbuildings but also the thousands of struc-tures that survived this unique earthquakeundamaged. Such a study would be of im-mense value to researchers, engineers andcode writers, enabling them to incorporatethis experience into better designed struc-tures in the future.

ACKNOWLEDGMENTSThe author appreciates the assistance of

the Mexican National Association of Pre-stressers and Precasters during his visit.Particular help was received from Mr. MarioFastag of Pretesca Group, Mexico City,producers of architectural precast concreteand GFRC and from Mr. Aurelio Zugasti ofTiconsa, manufacturers of the precast com-ponents for the fertilizer plant in L'azaroCardenas.

34

Fig. Al. Eleven-story apartment buildingon Amsterdam Avenue.

APPENDIX A -BUILDINGS IN MEXICO CITY

The following is a description of some ofthe buildings inspected in Mexico City afterthe earthquake:

— Eleven-Story Apartment Building— Seven-Story Parking Garage— Four-Story Parking Garage— Abraham Ayafa Gonzalez

Auditorium— Ten-Story Parking Garage— Five-Story Parking Garage

Eleven-Story ApartmentBuilding

This structure, which is located at No.210 Amsterdam Avenue (Fig. Al), was builtin 1979 using Spancrete hollow-core slabswith a 5 cm (2 in.) topping. The columnsare cast in place. In the lower five stories,concrete block masonry partitions were used,

and in the upper six stories, the partitionswere of gypsum drywall.

No structural damage was observed onthis building except for cracking in the stairsat the junctions of inclined stair slabs andthe horizontal landings. Cast-in-place stairsusually act as vertical trusses with high rig-idity, and not until the stairway is damageddoes the flexible frame participate in lateralresistance. There was moderate to extensivediagonal cracking in the concrete masonrypartitions (Fig. A2) in both directions; how-ever, no cracking was observed in the gyp-sum partitions.

Seven-Story Parking GarageThis structure, situated at Moreno and

Quantaneros Streets, is located in an areaof the city where moderate damage oc-


Fig. A3. Seven-story parking garage at Moreno Street.

curred during the earthquake (Fig. A3). Thestructural system has three 17 m (56 ft) spansof prestressed single tees supported on in-verted tees on the interior and L-beams atthe exterior ends. These in turn are carried

Fig. A4. Cracked buttressing wall atgarage entrance.

by precast concrete columns. Cast-in-placeconcrete is used generously to tie the pre-cast elements together to create frame ac-tion for lateral resistance.

Architectural precast concrete spandrelpanels are attached to the structure all aroundthe periphery. There are no signs of dis-tress in the garage, although there is am-ple evidence of distortions during theearthquake as seen in the cracked buttress-ing wall at the entrance to the garage (Fig.A4).

Four-Story Parking GarageThis structure is located at Antonio Anza

and Cuauhtemoc Avenue (Fig. A5) acrossthe street from the General Hospital col-lapses and adjacent to the MultifamilyHousing Complex collapse. The lower storyof the parking garage is used for commercialspace and the upper three stories for park-ing.

The structural system: the slabs spanning15 m (50 ft) used 60 cm (2 ft) deep doubletees with 5 cm (2 in.) reinforced concrete

36

Fig. A5. Four-story parking garage in the zone of maximum damage.

topping supported on inverted T-beamswhich rest on precast columns with largecapitals. There are seven 15.25 m (50 ft)bays longitudinally and seven 11 m (36 ft)bays transversely.

The column to beam connections are castin place with protruding bars and bars in-serted through round cores left in the col-umns. The lateral resistance in the transversedirection is provided by the inverted teesinteracting with the columns to create frameaction. In the longitudinal direction (in thedirection of the double tees) heavy, 1.1 m(3 ft 8 in.) wide beams on all column linesprovide frame action with the columns. Thereare circular ramps at the center of the struc-ture.

The fascias on all floors around the pe-riphery of the parking garage are curved ar-chitectural precast concrete panels. Exceptfor several very minor separation cracks inthe ground story between the masonry fillerwalls and columns (Fig. A6), there is no signof any structural distress in this structurewhich is located in an area of most severedamage.

Abraham Ayala GonzalezAuditorium

This building, located at the GeneralHospital (Fig. A7), was constructed about 8years ago, with a seating capacity of about1000. The roof of the auditorium consists of


Fig. A7. Abraham Ayala Gonzalez Auditorium.

single tees spanning up to 25 m (82 ft). Thereis no sign of any distress whatsoever in thestructure.

Ten-Story Parking GarageThis structure, which is situated on

Flamingo Avenue is located in an area ofthe city which underwent considerabledamage (Fig. AS). All around the garage areseverely damaged structures, some withseveral upper stories collapsed. In theadjacent block two steel structures (the

Fig. A8. Ten-story parking garage onFlamingo Avenue. In background is thetilted twenty-one story steel structure.

twenty-one and thirteen-story Pino SuarezOffice Buildings) collapsed and their twenty-one-story steel neighbor is several feet outof plumb, as seen in Fig. A8. The structuralslab of the garage consists of precastprestressed double tees with a 12.2 m (40ft) clear span supported on 1 m (3.3 ft) wideinverted tees and cast-in-place concrete col-umns.

In the direction parallel to the doubletees, there are cast-in-place beams on thecolumn lines to create frame action withthe columns for lateral resistance. Thereis a significant number of concrete wallsaround the periphery. This ten-story park-ing garage does not show a single sign ofdistress.

Five-Story Parking GarageThis structure is located at the corner of

Alliende and Equador Streets. The east halfof the building is cast-in-place concrete whilethe west half of the structure was switchedto precast concrete for economic reasons.The precast part uses prestressed concretechannels with a 5 cm (2 in.) topping, precastbeams and precast concrete columns fivestories high. No signs of distress could beobserved in this building.

Several other buildings using precastcomponents were also inspected. However,they were located in areas in which no dam-age was registered to them or to any othertypes of construction.

38

APPENDIX B -STRUCTURES IN LAZARO CARDENAS

The following is a description of the in-spected industrial structures built of precastconcrete components at the fertilizer plantin Lazaro Cardenas:

— Giant Silos— Three-Bay Building— Two-Bay Building

Giant SilosThree giant precast concrete silos (a fourth

is now under construction) for storingfertilizer of pitched (A-frame) sections (Fig.B1) were constructed since 1978; each onemeasuring 68 m (224 ft) in width and 280 m

(918 ft) in length and 28 m (92 ft) inheight.

The three-hinged A frames [every 9.4 m(28.7 ft)] consist of two precast prestressedchannel beams 44.7 m (146.6 ft) long witha maximum depth at midspan of 1.8 m (5.9ft). The two channel beams are tied at thefooting level by post-tensioned beams. Thespread footings have sockets to receive themain beams. At each of the three hinges,neoprene plates are used to allow for rota-tion.

The length of each silo is subdivided intothree segments by expansion joints. L-shapedprecast prestressed purlins receive the as-

ASBESTOSSHEETS

STEEL BOLTSPURLIN

NEOPRENEPLATE

MAIN BEAMS

HINGE DETAIL B

3.28'

7"! 7"

DoT M

0

M

44 I^4SECTION A

224'

Fig. B1. Section of silo and details.


bestos structural sheets. To provide windand seismic bracing, similarly shaped pur-lins have been arranged diagonally betweenthe three-hinged arches to create horizontaltrusses for one-third of the length from eachend of the silos.

As a result of the earthquake, only a very

few purlins have fallen off in these foursilos. Also, some of the columns of thelongitudinal wall near the outside abut-ments settled up to 10 cm (4 in.) leavinga gap between these columns and the mainbeams. The silos withstood this earthquakeremarkably well.

Fig. B2. Section of two-bay building with lean-on bay.

Fig. B3. Middle column row of two-bay building.

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Three-Bay BuildingA three-bay building (two bays and a lean-

on) 58 m (190 ft) wide and 120 m (394 ft)long was recently completed. The two bayseach span 25 m (82 ft) (see Fig. B2). Thesloping, simply supported precast pre-stressed roof beams have channel sectionssimilar to those of the giant silos shown inFig. B1.

Also, purlins and asbestos roofing aresimilar to those in the giant silos. The col-umns are precast concrete. While the sidecolumns are 5 m (16.5 ft) high, the 19 m (62ft) high middle row columns are split at theirtop 4.5 m (15 ft) into a fork-like shape toreceive conveyors and the two roof beams(Fig. B3).

The lateral resistance is provided by thefour rows of columns acting as cantilevers.During the earthquake, several of the slop-ing roof beams shifted on their supports byas much as 20 cm (8 in.) (Fig. B4). Measuredafter the earthquake the exterior longitu-dinal walls shifted and the width of thebuilding increased by 10 to 12.5 cm (4 to 5

in.). Also, large mounds of thin material weredriven through the slab-on-grade joints in ageyser-like fountain.

Two-Bay BuildingA two-bay building 50 m (164 ft) wide

and 120 m (394 ft) long, also recently com-pleted, has a slightly sloping roof with sim-ilar simply supported channel section precastprestressed roof beams, purlins and asbes-tos structural sheets as the other buildings.The massive precast concrete columns rest-ing on spread footings and acting as canti-levers provide the lateral resistance for thestructure.

During the earthquake, the movement ofthe ground caused the initially horizontalslab-on-grade to become wavy with differ-entials from the lowest to the highest pointof more than 1 m (3.3 ft) as can be seen inFig. 19.

Some columns of the middle row settledcausing differentials relative to the exteriorcolumns up to 60 cm (24 in.). Roof beams

Fig. B4. Beam shifted 20 cm (8 in.) at top of column.


Fig. B5. Temporary cribbing for repair of support.

at three column locations required tempo-rary cribbing (Fig. B5) so that the beamseating could be repaired. However, not asingle structural element suffered seriousdistress or collapse.

A free-standing 5 m (16.4 ft) tall end wallof this building is out of plumb by 50 cm

(20 in.) and will have to be replaced.The exemplary performance of the pre-

cast concrete structures despite the largedifferential settlements was the result of thestatically determinate structural configura-tion in which differential settlements do notcause additional moments or shear.

NOTE: Discussion of this paper is invited. Please submit yourcomments to PCI Headquarters by September 1, 1986.

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