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1、A C 1 COMP*3L * I 0662949 0525L87 224 SEISMIC DESIGN AND CONSTRUCTION Compilation 31 American Concrete Institute Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:54:23 MSTNo reproductio
2、n or networking permitted without license from IHS -,-,- 3 9 14 23 A C 1 COMP*33 * I 0662949 0525388 160 m Seismic Design and Construction AC1 Compilation 31 Contents Rehabilitation of the Jordan River Concrete 32 Buttress Dam for Seismic Loads, by Tibor J. Pataky and Bradley G. Kemp (Concrete Inter
3、national, V. 15, No. 5, May 1993, pp. 55- 60) 36 Bay Area Rapid Transit: Concrete in the 1960s by Bernard L. Meyers and Stephen H. Tso (Concrete International, V. 15, No. 2, February 1993, pp. 45-49) 42 Precast Concrete Connection Details for All Seismic Zones by C. E, Wames (Concrete International,
4、 V. 14, No. 1 1, November 1992, pp. 36-44) Precast Concrete in Seismic-Resisting Building Frames in New Zealand by R. Park (Concrete International, V. 12, No. 11, November 1990, pp. 43-51) Current Bridge Seismic Retrofit Practice in the United States by Mehdi “Saiid“ Saiidi (Concrete International,
5、V. 14, No. 12, December 1992, pp. 64-67) Shearwalls- An Answer for Seismic Resistance? by Mark Finte1 (Concrete International, V. 13, NO. 7, July 1991, pp. 48-53) Seismic Evaluation of Reinforced Concrete Frame-Wall Buildings by Sashi K. Kunnath, Andrei M. Reinhorn, and Young J. Park (Concrete Inter
6、national, V. 11, No. 8, August 1989, pp. 57-61) Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:54:23 MSTNo reproduction or networking permitted without license from IHS -,-,- Preface
7、This AC1 Compilation combines material previously published in CONCRETE INTERNATIONAL Magazine to provide compact and ready information on a specific topic. The material in such a compilation does not necessarily represent the opinion of any AC1 technical committee - only the opinions of the authors
8、 of the compiled articles. However, the material presented here is considered to contain useful information for readers interested in the subject. M. “Saiid“ Saiidi Chairman, AC1 Committee 341 Earthquake-Resistant Concrete Bridges John W. Wallace Chairman, AC1 Committee 368 Earthquake Resisting Conc
9、rete Structural Elements and Systems Todd Perbix Chairman, AC1 Committee 369 Seismic Repair and Rehabilitation On the cover: A relatively new addition to the skyline of Minneapolis-St. Paul is the City Center/Multi- Foods Tower. This %story building required 400,000 sq ft of sand-blasted precast pan
10、els. Architect: Skidmore Owings general contractor: PCL; and precast contractor: Gage Brothers. American Concrete Institute, Box 194 50, Redford Station, Detroit, Michigan 4821 9 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=list
11、mgr, listmgr Not for Resale, 03/05/2007 01:54:23 MSTNo reproduction or networking permitted without license from IHS -,-,- A C 1 COMP*3L * I I Obb2949 0525190 819 W Concrete Buttress Dam he Jordan River Dam (Fig. 1) is a part of the Jordan River Power Development on Van- T couver Island, approximate
12、ly 50 km west of Victoria, B.C., Canada. Three types of dam were considered during the planning stage in 1912: con- crete gravity, masonry gravity, and re- inforced concrete buttress. Because of the shortage of naturally available and readily usable construction materials a decision was made to buil
13、d an Am- bursen type concrete buttress dam. The dam was constructed between August 1912 and October 1913.192 Under B.C: Hydros current dam safety program, comprehensive inspec- tions and reviews (CIRs) are carried out once every six years for high hazard dams. Such a CIR was carried out for the Jord
14、an River Dam in 1985 and the results reported in Reference 3. The major recommendations of the CIR re- port were to: 0 Complete the foundation investiga- tions started in 1985 O Assess condition and strength of the concrete in the buttresses and the up- stream slab Complete the dynamic analyses star
15、ted in 1985 Evaluation of existing structure Field non-destructive testing Ultrasonic pulse velocity (uPV) testing of Buttresses 38 and 40 was carried out in July 1986. UPV readings were taken at a grid of about 1.2 m. A total of 192 readings were taken for Buttress 38 and 136 for Buttress 40. A his
16、togram of UPV readings is shown on Fig. 2. A rather subjective interpretation of quality would be that a good portion of the concrete is of acceptable quality, but 20 to 25 percent of the UPV readings imply poor quality concrete. The UPV readings were correlated with compressive strength by con- duc
17、ting tests on samples prepared from 15 cores. The relationship between UPV on dry specimens and compressive strength is shown on Fig. 3. The general tendency for the UPV to be in direct proportion to compressive strength is quite apparent, but the scatter is wide, as indicated by a correlation coeff
18、icient of 0.32. The degree of saturation had a negligible effect on the readings. Laboratory tests on concrete Laboratory tests were conducted to ob- tain information on the physical prop- erties of concrete such as compressive, shear, and tensile strengths, modulus of elasticity, Poissons ratio, th
19、ermal coef- ficient of expansion, water absorption, and air void content. Compressive strength tests were car- ried out in accordance with ASTM C42- 84a. Thirty-one 146 mm diameter hori- zontal cores were drilled; of these, 28 were taken perpendicular to and 3 in the plane of the buttress. Strengths
20、 varied from a low of 6.25 MPa to a high of 38.7 MPa, with a mean of 18.1 MPa. To determine the shear strength of the concrete at horizontal construction joints, which appeared to be a potential source of weakness, twenty 203 mm di- ameter cores were taken with their axis SPILLWAY TOP OF PARAPET I-
21、EL 390. l S 7 W A L U W A Y BUTTRESS No. T Y P - below: Vertical exitation. NORMAL RESERVOIR LEVEL EL 386. Fig. 8 - General arrangement of new strengthening ele- ments on tallest buttress. 1- I 1-1 . -20M SHEAR TIES IOM-, I I J .5M *e- BUT TRESS PILASTER - O. 76% REINFORCEMENT Fia. 9 - Tvpicai Dilas
22、ter reinforcement. W Fig. 10 - Unfactored horizontal stress contours (seismic and dead loading), Dortion of frame alonci Dilaster line P5. Base support It is difficult to realistically represent the dam concretehedrock interface in a fi- nite element model. When using a base that is assumed to be fi
23、xed or pinned to the foundation at the node points, large tensile stresses appear at the toe and heel during upstream-downstream loading. To represent more realistically the lack of tensile strength in the foundation, a single buttress finite element model was constructed with gap elements pro- vidi
24、ng zero tensile capacity at the base. Resistance to upstream-downstream loading was provided by sliding friction only. Results showed that the high tensile stresses at the heel and toe did disap- pear, however the magnitude of the stresses higher up in the buttress did not change significantly. Mode
25、 combinations The modal analysis makes available a great number of modes of little practical significance. The square root of the sum of the squares (SRSS) method was used for obtaining the total effective stresses. For cross-valley loading of the single buttress model, it was found that the first f
26、ive significant modes contributed to the majority of the total effective stresses. The results of studies with the two di- mensional frame models also showed that for cross-valley excitation only five or six modes had to be added to obtain a reasonable estimate of the total seismic response. A facto
27、r of 1.1 was applied to the set of stresses/reactions obtained to account for the effect of the unused modes. For vertical seismic loading with the two dimensional model, it was found that at least six modes had to be added to obtain a reasonably complete seismic response. A factor of 1.3 was applie
28、d to the set of stresses/reactions obtained to account for the effect of the unused modes. Fig. 7 shows the deflected shape for the first significant mode for each load direction of the tallest two dimen- sional frame model. Haunch support The advantages of a connection be- tween the tops of pilaste
29、rs and the up- stream slab was studied. A single but- tress model with the haunch only later- ally supported at the buttress nose was compared with a similar model having this support in addition to lateral re- straint at the top of each pilaster. A sig- nificant decrease in stresses was noted. “Str
30、ut” slabs were hence used to pro- 6 AC1 COMPILATION Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:54:23 MSTNo reproduction or networking permitted without license from IHS -,-,- A C
31、1 COMP*31 * m Ob62949 0525194 464 m vide a connection between the upstream slab and the top ends of the pilasters. Optimization of pilaster/strut layout Pseudo-static hand calculation provided a total of nine evenly spaced pilaster/ strut frames. Optimization was achieved with iter- ative finite ele
32、ment analyses, the aim of which was to maintain generated but- tress concrete tensile stresses at fairly even and acceptable levels. Seven pi- lastedstrut frames resulted, which were unevenly spaced (Fig. 8) along the up- stream-downstream dimension of the buttresses. The uneven spacing of these fra
33、mes was found to promote develop- ment of tensile stresses of similar mag- nitude in the unsupported zones be- tween adjacent frames. For a cross- canyon MCE-generated ground motion, the principal tensile stresses in the orig- inal buttress concrete were limited to about 1400 kPa. Optimization provi
34、ded struts 0.7 m square and pilasters 0.7 x 0.6 m. Structural design of remedial works The design of all new reinforced con- crete members, with the exception of strut anchors, was carried out using the limit state method. Because the MCE was considered, the seismic load factor was taken as 1.1. Des
35、ign actions were attained after appropriate combination of gravity, hydrostatic, earthquake-in- duced, and thermal loads. Pilasters Pilasters provide stiffening and con- tainment for the basically unreinforced buttress concrete. The pilasters are made to act composite with the buttress concrete and,
36、 because of their vertical orientation, are perpendicular to postu- lated planes of weakness at horizontal construction joints where cracking is ex- pected to initite. To improve composite action with the buttresses, u-shaped “shear ties” are provided which pass through the but- tresses, acting as b
37、oth stirrups for the pi- laster longitudinal reinforcement and as shear reinforcement at the interface. For increased ductility, hoop ties are pro- vided around the longitudinal rein- forcement in the pilasters. The reinforcement ratio, as a per- centage of the pilaster cross-sectional area, varies
38、between 0.6 and 1.6 with an average of about O.S. Pilaster longitu- dinal reinforcement was sized to with- stand the entire elastic tensile force on the pilaster cross-section. Typical pi- laster reinforcement is shown in Fig. 9. Struts Struts are the most critical of the load- resisting elements of
39、 the seismic reha- bilitation system. In addition to cyclic tensiodcompression axial forces, they must also resist bending moments at the strut/pilaster joints. Struts are designed as beam-columns, supporting the com- posite pilasterhuttress members. Struts are made continuous from one side of the v
40、alley to the other by passing through holes cut in the buttresses. Due to the limited installation clearance, strut reinforcement has one conven- tional splice per span. The reinforce- ment ratio, as a percentage of the strut cross-sectional area, varies between 1.9 and 3.3 with an average of 2.4. T
41、he most heavily reinforced struts are at the sup- ports. Stress contours, unfactored for mesh density, of typical struts adjacent to supports can be seen in Fig. 10. Typ- ical strut reinforcement details are shown in Fig. 11. Slabs Slabs provide the uppermost support for the new structural frame sys
42、tem. Cross- valley load is transferred through the slab, in diaphragm action, to dowels em- bedded in the underside of the existing upstream slab. The dowels are epoxy coated for corrosion resistance. One end on each slab has a sliding support to minimize thermal stresses while the other end is fixe
43、d. Typical slab rein- forcing details are shown on Fig. 12. Buttress reinforcing strips Seismic loading in the upstream-down- stream direction was found to produce high tensile stresses in the upstream and downstream edges of the buttresses. The pilaster on the downstream edge is de- signed to have
44、sufficient tensile capacity to resist both the upstream-downstream and cross-canyon stresses. Along the upstream edge of ten of the highest but- tresses reinforcing strips were provided to assist in the carrying of the upstream- downstream seismic stresses. The buttress reinforcing strips are lo- ca
45、ted where the calculated tensile stresses exceed 1000 kPa. Longitudinal reinforcement is designed to supple- ment existing reinforcement in the but- tress haunches. Reinforcement dowels with hooks are provided to promote composite action with the buttress. These dowels extend into the buttress haunc
46、h to such depth as to develop the 20M STRUT 2.82% REINFORCEMENT Fig. 11 - Typical strut reinforcement. Fig.12 -Typical plan of slab reinforcement. 6 BUTTRESS Popovici, A.; Stematiu, D.; and Steve, C Earthquake Engineering for Large Dams, John Wiley and Sons, New York, 1985. 7. Jansen, R.B., “Behavio
47、r and Deterioration of Dams in California,” Transactions, Interna- tional Committee on Large Dams Congress, Is- tanbul, V. 3, Q. 34, R. 35, 1967. 8. Motsanelidze, N.S., StabilityandSeismicRe- sistance of Buttress Dams, Russian Translation Series S8, A.A. Balkema, Rotterdam, 1987. 9. Committee on Saf
48、ety Criteria for Dams of National Research Council, Safety of Dams, Flood and Earthquake Criteria, National Academy Press, Washington, 1985. 10. B.C. Hydro, “Jordan River Diversion Dam, Structural Analysis” BCH Report No. H1950, 1987. 11. Nordstrom, P.A.; Steby, B.; and Tarandi, T., “Aseismic Design
49、 of Mtera Dam,” Interna- tional Committee on Large Dams, New Delhi, Q. 51, R. 7, 1979. 12. Hall, W.J., and Newmark, N.M., Earth- quake Spectra and Design, Earthquake Engi- neering Research Institute, Berkky, D82. 13. Zanger, C.N., “Hydrodynamic Pressures on Dams Due to Horizontal Earthquake Effects,” Engineering Monograph No. 1 1, Bureau of Recla- mation, Denver, May 1952. Selected for reader interest b