11th INTERNATIONAL BRICKlBLOCK MASONRY CONFERENCE

TONOlI UNlVERSITY, SHANOHAI, CHINA, 14 - 16 OCTOBER 1997

INTERNAL FORCE ANAL YSIS FOR THE PILOT PROJECT OF 15 STOREY HIGH-RISE REINFORCED BLOCK RESIDENTIAL

BUILDING OF PANJIN STATE TAX BUREAU

Song Yang I

1. ABSTRACT

In view of the composition of materiais, the different hollow rates of walls and the characteristics of building constructions of small . concrete hollow block high-rise buildings, when we conduct their internai force analysis, especially the analysis of seismic action, we can not use the analysis programs for high-rise buildings directly. By comparison between the ca1culation models, load bearing performances of high-rise block structures and those of high-rise reinforced concrete shear wall structures , we used SATWE program for the internai force analysis of the pilot project of 15 storey high rise reinforced block residential building of Panjin State Tax Bureau. Although we finished the analysis, we met a lot of difficulties and problems, which show that it is necessary and urgent to develop the structural analysis program for reinforced block high rise buildings.

2. GENERAL SITUATION OF THE PROJECT

The pilot project of high-rise block residential building of Panjin State Tax Bureau is laid up with high strength small concrete blocks and special mortar. Rational arrangement of reinforcement and core columns is adopted for the structure, The building has 15 storeys and its total height is 45.5m. lts total floor area is 7002.5m2 and its typical floor area is 517.2m2 (see Figure 1). The strength grades ofwalling materiaIs and grouting rate are

KEY WORDS: reinforced masonry, internai force analysis, ca1culation of section

I Assistant engineer, China Northeast Building Design & Research Institute

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shown in TabIe 1.

TabIe 1. Walling materiaIs

Storeys Strength grade Strength grade Strength grade Grouting

of block of mortar of grout rate

1-2 Mu20 M20 C30 100%

3 - 8 Mul5 MI5 C25 70%

9 - Ii MulO MIO C20 70%

12 MulO MIO C20 70%

13 - 15 MulO MIO C20 100%

The project is located on the Class III site in the 7 degree seismic zone and the basic wind pressure is

O.605kN 1m2

Figure 1. Typical floor plan

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3. DETERMINATION OF STRUCTURAL CALCULATION SCHEME

By comparison of load-deformation curves of various members of the experiments on concrete small hollow block wall from the domestic institutions in China (I. e. research on seismic performance of reinforced concrete small block high cantilevered shear wall and on normal section static force and seismic performance of reinforced concrete small block shear wall) and the load deformation curves of reinforced concrete shear wall of the experiments conducted by Qinghua University, we can see that both ofthem are very similar, only the descending section of the curves of concrete small block shear wall drops quickly, i. e. its load bearing capacity drops quickly. This is because both ofthem are different in construction. The horizontal reinforcement for concrete small hollow block masonry only can be placed in bed joints, and when load reaches to the ultimate load f or the masonry the bed joints in the bottom course of the wall have already cracked, so we can see that the restraint effect of the horizontal reinforcement in the compression zone of the masonry is not as obvious as that of horizontal reinforcement of reinforced concrete shear wall.

The grout adopted for this project is special grout, which is high in mobility, low in shrinkage, high in strength and strong in cohesion with blocks and mortar, The bearing capacity of the masonry, which : is laid IIp with the high strength blocks, good performance mortar and grout, is similar to that of reinforced concrete shear wall, Therefore, the calculation program for reinforced concrete shear wall can be adopted for the internai force analysis ofthe building.

4. CALCULATION AND ANAL YSIS OF STRUCTURAL INTERNAL FORCE

The structuraI calcuIation program adopted for this project is the SA TWE programo As the program is based on the wall element theory to form a kind of universal wall element for imitating shear wall, it can well imitate the real load bearing performance of the shear wall of a building, as well as no limitations on the dimensions and locations of the openings in shear wall, so i~ is suitable for the calculation of this pilot project.

As the materiais of the concrete small hollow block masonry are different from the materiais of reinforced concrete shear wall and the elastic modulus and rigidities of them are also different from each other, so the SATWE program can not be used directly for the calculation. Based on the equivalent principIe of wall rigidity, the program can be used by converting the elastic modulus of block masonry into the e1astic modulus of concrete, in order to simpIify the calculation, based on the principie that the result by multiplication of the elastic modulus and the thickness of the wall is a constant, the thickness of the corresponding C20 reinforced concrete shear wall can be calculated ,The elastic moduIus of the concrete small hollow block masonry can be calculated according to the following formula:

E=O.8f.i!f.lzX500!c+ f.i/d=400f.iIl·ifc+ f.i/d

where f.i! - hollow rate of concrete small hollow bIock

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(1)

JIz - grouting rate

fJ,3 - coefficient of mortar grade lo - characteristic compressive strength of grout in cube fd - design value of compressive strength ofhollow block masonry

And then, add part of wall weight, which is caused by the change in the wall thickness and unit weight to the wall with inverse sign, so as to ensure that the self-weight of the wall remains unchanged. Afier above preparation, we can use SA TWE program t() conduct the ca1culation. During ca1culation of the project, we consider the tortional couple effect and take the lower limit of the program, i.e. 0.55, in consideration of the actual working state. Through calculation, we obtain the internai forces of members, structural vibration cyc1e and displacement and etc.

4.1 Structural vibration cyc1e

Tj=0.5847 (s) T.=0.1833 (s) TFO.1154 (s)

T]=0.5261 (s) T5=O.l725 (s) Ta=0.0996 (s)

T/ n=O. 5 847/14=0.042

T]/n=0.5261114=0.038

T Yn=0.50 16/14=0.036

T3=0.5016 (s)

T ?O.l740 (s) TrO.0877 (s)

The ca1culated cyc1e is basically within the rational range.

4.2 The total base shear under the action of earthquake

X direction: Qox=3594.885 (KN)

Qo,/Ge=3 .40%

Mox= I 02044.422 (KN-m)

Y direction: Qoy=3833.393 (KN)

Qo/Ge=3 .62%

Moy=107147.883 (KN-m)

4.3 The structural top displacement and the maximum displacement between storeys under the action of earthquake and wind load meet the design requirements of codes, which are listed in Table 2. .

5. SECTION COMPUT ATION OF MEMBERS

The computation formula for section of concrete small hollow block masonry is different from that for section of reinforced concrete shear wall. The section

computation of the members of this project is conducted on the basis of the formula

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obtained form the experiment on the normal section and oblique section of concrete

small hollow block masonry.

Table 2. The Displacement

Top displacement Displacement between storeys

U(mm) UIH Allowable value ~U/h Allowable value

Wind load X direction 2.84 1/9999 1/1000 1/9999

Y direction 1.56 1/9999 1/1000 1/9999

Earthquake X direction 6.69 1/7013 1/900 1/5212

Y direction 7.10 1/6602 1/900 1/3604

5.1 Normal section ca1culation ofthe wall

(1) First, large or small eccentric compression shall be determined. when X:;;çbho, it is defined as large eccentric compression;

when X>~bho, it is defined as small eccentric compression;

(2) For large eccentric compression, the following formula shall be used:

N~(fi,bx+f' yA 's-fyA.-Ifs;AsJ/YRE

Ne~ffi,bx(ho-x/2)+/y 'A. '(ho-a. ')-Ifs;S.J/YRE

1/900

1/900

1/800

1/800

(2)

(3)

where fi, - design value of compressive strength of masonry in bending, take fi, = J. 2f

when x<2a's

Ne '~UyAs(ho-a 'J}/YRE

(3) For small eccentric compression, the following formula shall be used:

N~{fbx+f'yA 's-a,As}/YRE

Ne~{fbx(ho-x/2)+f'yA 's(ho-as ')}/YRE

as=/y(x/ho-O.8)/(Çh-O.8)

(4)

(5)

(6)

(7)

Through the internai force ca1culation by the SA TWE program and the large and small eccentric compression calculation with the formulas mentioned above, it is shown that the vertical reinforcement ofthe wall ofthe project meets the calculation requirement.

5.2 Normal section calculation ofthe coupling beam

MS/yAs(ho-as ')/YRE (8)

Through ca1culation, it is shown that the horizontal reinforcement of the coupling beam

of the project meets the ca1culation requirement.

5.3 Oblique section calculation ofthe wall

First, to ca1culate and check ifthe wall section meets the requirement.

Vw50. 4bhjll2 /YRE (9)

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The bearing capacity of wall oblique section is calculated according to the following formulas:

(1) For eccentric compression wall,

Vw5{{[O.264-0. 116M1(VhoJ}bhol/2+o. 12NA,./A +O.8fyvAshhls}/YRE (10)

(2) For eccentric tension wall,

Vw5{{[O.264-0.116M1(VhoJ}bhol/2-O.12NA,./A +O.8fyvAshhls}/YRE (11)

Through calculation, it is shown that the horizontal reinforcement of the wall of the project meets the calculation requirement.

5.4 Oblique section calculation ofthe coupling beam

First, to calculate and check if the coupling beam section meets the requirement.

(1) When span-depth ratio is larger than 2.5,

Vbg).28bhol/2/YRE

(2) When span-depth ratio is smaller than 2.5,

Vbg). 22bhol/2/YRE

(12)

(13)

The oblique section bearing capacity of the coupling beam is calculated according to the following formulas:

(I)When span-depth ratio is larger than 2.5,

V ~(O. 066bhol/2 +0. 8fyvAsvhls}/YRE

(2)When span-depth ratio is smaller than 2.5,

Vb5{(O. 058bhol/2 +0. 7fyvAsvhls)/YRE

(14)

(15)

Through calculation, it is shown that the oblique section and reinforcement of the coupling beam of the project meet the calculation requirement.

6. CONCLUSION

(l)Through the calculation for the project, we can see it is completely possible to build high-rise buildings with high strength concrete small hollow blocks and with engineered materiais and technology.

(2)The calculated cycle and seismic force are ali within the rational range.

(3)Although the SATWE program can be used for calculation of reinforced masonry structure, it will cost a lot of time and labor in calculation, so we think it is necessary and urgent to develop the special program for the structural analysis of reinforced block high-rise buildings.

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7. REFERENCES

1. « Specification for Design of Reinforced Masonry Structures» (in discussion

stage) 2. « Specification for Design and Construction of Reinforced Concrete High Rise

Structures » 3. « Research on Seismic Behavior of Reinforced Concrete Small Block High

Cantilevered Shear Wall » 4. « Research on the Normal Section Static Force and Seismic Behavior of

Reinforced Concrete Small BlQck Shear Wall »

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