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Concrete In Australia : June 2013
Concrete in Australia Vol 39 No 2 31 懸 噺豹拳穴捲 噺 拳怠豹œÆº講捲 詣穴捲 噺 拳怠岾挑 訂峇̊æœ訂掴 挑 拳怠詣 講 L x v 兼 噺豹懸穴捲 噺 拳怠磐詣 講卑豹̊æœ講捲 詣穴捲 噺 拳怠岾挑 訂峇態 œÆº 訂掴 挑 L x 拳怠磐詣 講卑態 m 継荊肯 噺豹兼穴捲 噺 拳怠磐詣 講卑態豹œÆº講捲 詣穴捲 噺 拳怠岾挑 訂峇戴 ̊æœ 訂掴 挑 拳怠磐詣 講卑戴 L x 継荊肯 継荊絞 噺豹肯穴捲 噺 拳怠磐詣 講卑戴豹̊æœ講捲 詣穴捲 噺 拳怠岾挑 訂峇替 œÆº 訂掴 挑 L x 拳怠磐詣 講卑替 継荊絞 Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. 拳噺拳怠œÆº講捲 詣 w = equivalent traffic lane loading w1 L x w Several standardised precast concrete bridge construction systems are available to meet this replacement demand, including some that are nearly fully precast and do not require an insitu concrete deck. ese have become known (in NSW at least) as "Modular Bridges". Unfortunately, some of the available Modular Bridge construction systems have not been fully compliant with the relevant design standard AS5100-2004. Nevertheless, their use in NSW has been permitted by the then RTA (now RMS), subject to a limited Annual Average Daily Traffic (AADT) and a reduced design life. Recently, a new Modular Bridge construction system that fully complies with AS5100 has been developed and utilised. is system, which has been adopted as a typical background structure on which to superimpose the analysis methods proposed in this article, takes advantage of elastomeric shear keys, which are seen to offer the following benefits: 1. ey are not reliant on the long term viability of concrete or mortar infill keys, which are subjected to many daily stress cycles due to live load, daily and seasonal temperature effects, and seasonal and long term shrinkage effects, and whose replacement involves temporary bridge closures. 2. Transverse prestress may be applied immediately, without waiting for the joint to gain strength. 3. e shear key acts as a backing strip to support sealant applied over it. 4. is sealant, not being required to accommodate significant movements, does not require a bond breaking tape beneath it. 5. e elastomeric shear key provides an unambiguous full shear, zero moment condition, allowing confidence in the design assumptions. 6. e structural effectiveness of the shear key is not reliant on the sealant. 7. If anticipated, the elastomeric shear key may permit the super-structure to be demountable and relocatable. While post-tensioned transverse ribs with stressed insitu joints between deck-beams are feasible, and in the appropriate circumstances, preferable, the most common and most economical configuration of the system, is that which utilises elastomeric shear keys between deck-beam units. Further, it is suggested that this configuration allows the structural analysis to be carried out relatively simply, without resort to computer based grillage analysis (as would be appropriate for the full width prestressed concrete transverse rib configuration), which of course, nevertheless remains an option. In the following sections, this relatively simple analysis is presented for single lane bridges (two 2100 mm-wide deck beam units), and double lane bridges (four 2100 mm-wide deck beam units). Typical bridges of this type are shown in Figures 1-4. 2.0 BASIS OF STRUCTURAL ANALYSIS Figures 5 to 9, show sequentially, the load, shear, moment, rotation and deflection, resulting from the load in the form of the first term of a Fourier series. Rather than add terms to this series, in order to make the load Nominal Length Simply Supported Span M1600 Moment w1 = M(π/L)2 10m 9.6 m 783 kNm 84 kN/m 12m 11.6 m 995 kNm 73 kN/m 14m 13.6 m 1354 kNm 72 kN/m 16m 15.6 m 1716 kNm 70 kN/m 18m 17.6 m 2206 kNm 70 kN/m 20m 19.6 m 2742 kNm 70 kN/m Table 1. Nominal deck beam lengths. Figures 5-9. Sequentially, the load, shear, moment, rotation and deflection, resulting from the load in the form of the first term of a Fourier series.