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8 Construction Loading in High-Rise Buildings S.K. Ghosh, Ph.D., P.E.* 8.1 Introduction ........................................................................8-1 8.2 Construction Loads.............................................................8-1 Design Considerations • Field Veriﬁcation • Reﬁned Analysis 8.3 Properties of Concrete at Early Ages ...............................8-19 Compressive Strength • Tensile Strength and Bond Strength • Punching Shear Strength • Modulus of Elasticity • Shrinkage of Unreinforced (Plain) Concrete • Creep of Unreinforced (Plain) Concrete • Effects of Drying on Flexural Cracking 8.4 Strength Consequences of Construction Loads..............8-37 Safety Analysis • Reﬁned Safety Analysis 8.5 Serviceability Consequences of Construction Loads......8-47 Causes of Excessive Deﬂections • Components of Long-Term Deﬂection • Experimental Investigation • Control of Slab Deﬂections 8.6 Codes and Standards.........................................................8-55 References .....................................................................................8-55 8.1 Introduction Structural formwork and its support system must be given careful consideration in two different respects: (1) loads that are applied to the formwork and its supports, and (2) loads that the formwork and its supports apply to the structure. The ﬁrst is the subject of Chapter 7 on formwork and falsework; the second is the subject of this chapter. 8.2 Construction Loads 8.2.1 Design Considerations In the construction of multistory buildings with reinforced concrete ﬂoor slabs, a step-by-step sequence of operations is employed. The sequence is comprised of the steps of setting up shoring on the most recently poured ﬂoor, forming the next ﬂoor, setting up reinforcement, and concreting the slab. Because the ﬂoor below the one being concreted is usually only a few days old, it is common practice to leave * President, S.K. Ghosh Associates, Inc., Palatine, Illinois, and Fellow of the American Concrete Institute; specializes in structural design, including wind- and earthquake-resistant design. 8-1 © 2008 by Taylor & Francis Group, LLC 8-2 Concrete Construction Engineering Handbook T Days 2T Days 3T Days 3T + n Days i i –1 i–2 i–3 i–4 4T Days Basic Operations Place Floor i Remove Shores Under x days Floor i – 2 x + n Days FIGURE 8.1 Construction sequence using three levels of shores. formwork supports in place between that ﬂoor and a small number of ﬂoors below it. A typical con- struction cycle using three levels of shores is illustrated in Figure 8.1. In discussing construction loads, it is convenient to express them as a factor times the sum of the self-weight of the ﬂoor and the dead load of the formwork. The term floor loading ratio is used for this factor. Progressive slab deﬂections that had been causing problems in Sweden in the early 1950s led to the ﬁrst study by Nielsen (1952) of a rational approach to stripping formwork for ﬂoors. Nielsen gave a detailed analysis of the distribution of load between a system of connected shores and ﬂoor slabs. The met

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