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OCR for page 130
130 be used in the load-bearing wall at 0.3-m vertical guidelines. The most important features to be confirmed by spacing. the experiments follow: Both a minimum ultimate tensile strength and a mini- mum tensile stiffness of the reinforcement should be Allowable design pressure. The allowable design sill specified to ensure sufficient tensile resistance at the pressure as affected by sill width, sill clear distance, soil service loads, to provide adequate ductility, and to friction angle, reinforcement spacing, truncated base, ensure a sufficient safety margin against rupture fail- and sill type (especially an integrated sill) should be ure. A recommended procedure for determining the confirmed. Some attention should also be given to the required minimum tensile stiffness (at 1.0 percent effect of construction sequence (i.e., the potential bene- strain) and the minimum ultimate tensile strength are fits of constructing the upper wall before placing the stipulated. bridge superstructure). It is recommended to extend the reinforcement lengths Long-term performance of GRS bridge abutments in the in both the upper and lower walls, at least the top three in-service condition. It is suggested that the design layers of each wall, to about 1.5 m beyond the end of the method and construction guidelines be implemented in approach slab to promote integration of the abutment bridges on secondary roads with simple (yet reliable) walls with the approach embankment and the load-bear- instruments to monitor their long-term performance. ing abutment, so as to eliminate the bridge "bumps"--a Offset between the facing blocks and the centerline of chronic problem in many bridges. bridge bearings. The analysis conducted in this study Connection strength is not a design concern as long as has indicated that an offset less than 0.9 m (3 ft) (as sug- the reinforcement spacing is kept not more than 0.2 m, gested by the NHI manual) would not cause any adverse the selected fill is compacted to meet the specification effects. The effect of an offset of 0.8 m (e.g., 0.2 m of stipulated in the recommended construction guidelines, block depth + 0.3 m of clear distance + 0.3 m of half- and the applied pressure does not exceed the recom- sill-width) may be selected for testing. mended design pressures in the recommended design Preloading and/or pre-stressing of GRS abutments. method. Simple measures of preloading and/or prestressing has been shown effective at increasing significantly the load-carrying capacity of a GRS abutment and reducing SUGGESTED RESEARCH the sill settlement from two- to fivefold (depending on the fill placement condition) and the lateral movement It is suggested that a series of full-scale experiments of by about threefold. A cost-effective procedure and GRS bridge abutments be conducted to confirm the overall proper specifications for preloading and/or prestressing validity of the recommended design and construction have not been established.