《ACI-COMPILATION-26-1994.pdf》由会员分享，可在线阅读，更多相关《ACI-COMPILATION-26-1994.pdf（86页珍藏版）》请在三一文库上搜索。
1、 A C 1 COMP*:26 $1: m Ob62949 0535888 639 m FORMWORK Compilation 26 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 02:30:18 MSTNo reproduction or networking p
2、ermitted without license from IHS -,-,- A C 1 COMPf2b ft Ob62949 0515889 575 = Preface AC1 Compilations combine material previously published in Institute periodicals to provide compact and ready reference on specific topics. The Material in a compilation does not necessarily represent the opinion o
3、f an AC1 technical committee - only the opinions of the individual authors. However, the information presented here is considered to be a valuable resource for readers interested in the subject. Samuel A. Greenberg Chairman, AC1 Committee 347 Formwork for Concrete On The Cover: A self-spanning steel
4、 forming system was of considerable help in speeding con- struction of a new basketball arena for the University of Arkansas, Fayetteville. With each bent cast in one piece, erection of the support for the cantilevered tier of seats and the roof progressed at almost two bents per day. The building s
5、cale for the 18,000 seat Bud Walton arena was de- signed so as not to dominate other buildings on campus. (See article starting on p. 39.) American Concrete institute, Box 191 50, Redford Station, Detroit, Michigan 4821 9 Copyright American Concrete Institute Provided by IHS under license with ACI L
6、icensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 02:30:18 MSTNo reproduction or networking permitted without license from IHS -,-,- A C 1 COMPa26 Xt m 0662949 0535890 297 m 3 8 15 21 28 33 39 Formwork AC1 Compilation 26 Construction Live Load Caused by Powered 42 Bu
7、ggies, by Hui-Ming Lee, Wai-Fah Chen, and Xi- La Liu Interactive Vertical Formwork Selection System, by Awad S. Hanna and Victor E. Sanvido 47 Construction Load Analysis of Slabs and Shores 52 Using Microcomputers, by Pericles C. Stivaros and Grant T. Halvorsen 55 Interactive Horizontal Formwork Sel
8、ection System, by Awad S. Hanna and Victor E. Sanvido 60 Shore and Reshore Scheduling Using a Microcom- puter, by N. J. Gardner and A. Muscati 66 Textile Form Method to Improve Concrete Dura- bility, by Marton Marosszeky, Michael Chew, 76 Massi Arioka, and Phillip Peck Steel Forms Speed Construction
9、 o Upper Deck Bents or University Basketball Arena, by Russell Brown and Matt Boone 78 Formwork for Architectural Concrete at North River Water Pollution Control Plant, by Martin Fradua and Ted Long Formwork Removal and Architectural Concrete, by Joseph A. Dobrowolski Formwork Release Agents Air-Sup
10、ported Forming: Will It Work?, by Robert B. Haber Movable Air Form Structures for Containing Air- borne Releases, by Richard A. Kaden Fabric Forms for Concrete, by Bruce A. Lamber- ton Modular Structural Forming System for Shotcrete, by Dale Pearcey Precast Concrete Stay-in-Place Forming System for
11、Lock-Wall Rehabilitation, by James E. McDonald Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 02:30:18 MSTNo reproduction or networking permitted without license from IHS -,-,- Construct
12、ion Live Load Caused by Powered Buggies otor-driven buggies are widely used to transport the ready-mixed concrete M in the construction of re- inforced concrete buildings. In gen- eral, the buggies travel on very young concrete slabs and are the main source of construction live load. In a traditiona
13、l formwork de- sign, buggies are treated as a uni- formly distributed load of 75 psf (3.58 kPa), but there are few theo- retical justifications for using this design live load. Since most con- struction disasters occur while con- crete is placed, it is necessary to in- vestigate the actual effects o
14、f con- crete buggies on construction safety. A practical formwork system de- sign subjected to live load caused by powered buggies has been exam- ined. To this end, a realistic calcu- lation model considering the effects of formwork decking, and wooden joists, stringers, and shores has been establis
15、hed. The interaction between the structural components and the con- struction loads has been studied for different concrete ages. The results show that if more than two buggies are used in the same floor span, the applied load on shores can be greater than the design limit. Con- crete age has little
16、 influence on the load distribution. The effects of decking, joists, and stringers can reduce the bending moment of con- crete slab by about 7 percent and increase the axial forces of shores by about 2 percent. The end rc- straint effects of the connected slab- beams or the load distribution also ha
17、ve been studied. Research significance Numerical studies of the effects of combinations of variables such as construction techniques, material properties, weather forces, and rate of construction operation on the load distribution of the supporting system have shown that construc- tion live loads ha
18、ve the most signif- icant influence. Since motor-driven buggies are the main source of the construction live loads, ideally, this design live load should be derived by a rigorous structural analysis and defined on a statistical basis. Theoretical and statistical evi- dence to define the live loads i
19、n this way is not yet available, so they have been taken as equal to a uni- formly distributed load of 75 psf (3.58 kPa) as laid down in current regulations. Attempts have been made here to provide some theoret- ical justifications about design live load due to powered buggies in a practical formwor
20、k system. It has been found that a design value 85 psf (4.06 kPa) is more realistic than that of the present in-service value of 75 psf. Impact load caused by buggies It is well-known that substantial impact loads can be generated when the buggies travel at some speed. The impact live load acts on t
21、he partially hardened slabs and the supporting formwork system. Ac- cording to the AASHTO Standard Specification for Highway Bridges (1989), the impact load factor can be calculated by of moment* (i) (2) (3) (3) 4.30 4.28 4.33 .993 Shore Loads (kip) - real limit shore jorcr . 2.0 design limil 1.5 4
22、0.5 . O 1 I 11.40 I 11.36 I 11.52 I .WO 0.0 I I O 1 2 3 4 5 No. of Buggies 4 (a). t = Y days Shore Loads (kip) 4 .o 3.5 I 5.25 I 5.43 I 5.50 I .954 3.0 2.5 2.0 1.5 1 .o 0.5 design limil 0.0 I J 0 1 2 3 4 5 No. of Buggies (b). 1 = 5 days Share Loads (kip) 4.0 I I 3.5 - 3.0 - real limil 2.5 - 2.0 - de
23、sign limit 1.5 - 1.0 - 0.5 - 0.0 0 1 2 3 4 5 No. o1 Buggies (c). t = 7 days Fig. 4-Maximum shore loads versus number of buggies. -20 auadablc bending capacity -30 I I 0 1 2 3 4 5 N . or Buggies (a). t = Y days ending Mornent kip-fi) 30 I auailabit bendrng eopacify 20 Table 1 - Maximum shore loads, k
24、ips Table 2 - Maximum bending moment, kip-ft 2 7 89 8.04 8 i3 .970 3 1 1 10:28 I 10.51 1 10:64 I .%6 FORMWORK Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 02:30:18 MSTNo reproduction o
25、r networking permitted without license from IHS -,-,- A C 1 COMP*2b * m Obb29Y9 0515894 932 m r Strain Stress Fig. 6-Strain and stress distributions at slab-beam intersection. coefficient dependent on concrete age, temperature, and cement type. According to Gardner (1985), 0 can be determined by Tab
26、le 3. The comparisons between slab loads and resistances for different concrete ages and different number of buggies are shown in Fig. 5. The results show clearly that the maxi- mum bending moments caused by buggies will not exceed the slab ca- pacity. That is, while concrete is placed, the most dan
27、gerous parts are the shores, especially the shore at midspan. The results also show that the de- sign live load of 75 psf (3.58 kPa) only allows for one buggy on each slab; therefore, when the number of buggies on one span exceeds one, the in-service design value of 75 psf (3.58 kPa) is questionable
28、. In gen- eral, it is appropriate to consider two buggies in the same span, so the minimum design live load should be (3177 + 1875) 75 psf 4500 L = = 84.2 psf (4.03 kPa) where shore live load = 3177 Ib and shore dead load = 1875 lb. There- fore, it is recommended here that the live load for formwork
29、 design should be 85 psf (4.06 kPa) and us- ing more than two buggies on the same span should be avoided. Table 3 - Development of concrete strength (Gardner, 1985) - Age, days 2 3 4 5 6 7 8 9 10 11 12 13 14 21 28 1, 73 F (22.8 C) 0.31 0.47 0.59 0.66 0.72 0.76 0.79 0.81 0.83 0.85 0.86 0.88 0.89 0.90
30、 0.96 1 .o0 vpe I cement 55 F (12.8 C) 0.15 0.28 0.40 0.49 0.57 0.63 0.68 0.72 0.75 0.77 0.80 O. 82 0.84 0.86 0.94 1 .o2 40F (4.4 C) 0.03 0.11 0.18 0.24 0.32 0.39 0.44 0.48 0.52 0.56 0.59 0.62 0.64 0.67 0.80 0.88 73 F (22.8 C) 0.54 0.65 0.74 0.78 0.81 0.83 0.85 0.86 0.88 0.89 0.90 0.91 0.92 0.92 0.9
31、7 1 .o0 Note: For a given treatment, can be obtained by a linear interpolation. pe II cemeni 55 F (12.8 C) 0.33 0.50 0.62 0.66 0.70 0.73 0.75 0.77 0.79 0.81 0.82 0.84 0.86 0.86 0.93 O.% 40F (4.4 C) 0.11 0.30 0.43 0.54 0.63 0.70 0.77 0.80 0.82 0.84 0.86 0.88 0.89 0.90 0.99 1 .O7 Influence of the form
32、work In recent years, several calculation models have been proposed to sim- ulate the actual construction proc- ess of flat plate concrete multistory buildings see, for example, Liu, Chen, and Bowman (1985) and Mosallam and Chen (1 990) J , but all ignore the effects of formwork decking, joists, and
33、 stringers. In the present study, the results of consid- ering and neglecting these effects are given and compared to deter- mine their actual influences on the load distribution. After slab concrete has been cast on the formwork decking, the con- crete gains its strength gradually with time. When a
34、n external load is applied, the formwork decking and the partially hardened slab work to- gether to support the load. To in- clude the interaction of concrete and wooden decking in an analysis, the wood has been transformed into an equivalent concrete contribu- tion. Under uniaxial forces, the decki
35、ng section area can be trans- formed into equivalent concrete section area by E, E, A = - A , When the bending moment caused by the transverse load is consid- ered, the strain and stress distribu- tion at a cross section of the slab- beam is shown in Fig. 6. The posi- tion of neutral axis can be det
36、er- mined by X, + X, = h, + h, (6) 1 1 - E , x = -E,X; 2 2 1 2 + -E, (2x2 - hJh, (7) Thus, the equivalent concrete slab beam has a nominal height of 2x, and the nominal elastic modulus is Ecr In Table 4, the results consider- ing the effects of the formwork sys- tem and those that did not are com- p
37、ared, showing clearly the effects of formwork decking, joists, and stringers. The axial shore loads are increased by about 2 percent and the maximum bending moments are decreased by about 7 percent. This indicates the formwork system transfers very little load from the slab to shores. Although the e
38、rror is small, a more realistic result can be achieved simply by modifying the results obtained from the usual cal- culation models adopted by Liu, Chen, and Bowman (1985) and by Mosallam and Chen (1990) by a co- efficient 1.02 for shores and 0.93 for concrete slabs. Restraint effect A building has
39、more than one span; hence, load distributions for slabs will be affected by other slabs. The models used by Liu, Chen, and Bowman (1985) and Mosallom and Chen (1990) neglect this restraint effect. No work has been reported on the study of this influence. According to the current equiva- lent frame m
40、ethod for designing two-way slabs, we shall consider at 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 02:30:18 MSTNo reproduction or networking permitted without licen
41、se from IHS -,-,- A C 1 COMP*2b * Obb2949 0515895 879 m Loading condition* 1 buggy, I shore load, kips Table 4 - Comparison of present model with Mosallamc (1990) model Modams Present model model fi (1) (2) (2) 1.632 1.613 1.012 1 and2 4 buggies naximum shore between Points *Positive moment indicate
42、s tensile stress at top of siab; negative moment indicates tensile stress at bottom of siab. - moment 1.949 1.866 1.044 3.177 3.176 1.OOO shore load + moment 2.130 2.131 0.999 - moment 5.198 5.194 1.001 least three spans of slabs. Thus, when the load distribution of a slab is calculated, the end-res
43、traint ef- fects of at least two slab beams di- rectly connected to each other must be considered. To evaluate the end- restraint effect, the internal forces of three-span and one-span models under the same loading conditions are used. The comparisons are listed in Table 5, where it can be seen that
44、 the end-restraint effects have little influence on the load distribution (-Y, m AC! COMPILATION 22 Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 02:30:18 MSTNo reproduction or networki
45、ng permitted without license from IHS -,-,- A C 1 COMP*E!b * 0bb2949 0535933 841 = them. The three foot modules can be forped with 30 x 30 in. domes and 6 in. ribs. The preceding sections presented five different horizontal formwork systems and two special ones, joist and waffle slab formwork system
46、s. Two of these systems - the con- ventional wood system and the con- ventional aluminum system - are classified as hand-set systems. The remaining systems are classified as crane-set systems. Joist-form and dome forms can be handled by hand or attached to the surface deck of the flying form and flo
47、wn as a unit. Factors affecting selection of formwork systems There are several ways to form any given concrete building. One of them will typically be the lowest cost method. Selecting the lowest cost method of formwork requires searching through a maze of forrn- work systems and their attributes.
48、The construction cost of slabs is often more than half the cost of structural framing systems, except in extremely tall bildings. Selec- tion of the floor formwork system therefore deserves considerable at- tention to minimize cost. Types of slabs The selection of a formwork system should be made on the basis of the selected floor system that satisfies the structural loading conditions. Floor slabs in concrete buildings are classified into two basic types, based on the load distribution ap- plied on the slab: Two-way slabs, in which the rec- tangularity ratio (slab length/width) is between 1