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Monotonic shear loading tests were conducted on three half-scaled reinforced concrete deep beams with shear span-todepth ratios of 0.5 to 0.75. The obtained test results were investigated in detail based on the experimental measurements and finite element analysis. From these investigations, a new macro model for deep beams was established. This model is composed of two crooked main struts formed between both beam end sections and branched-off sub struts. The compressive force introduced to main struts balances the flexural compression and the external shear force. The bond stress of the longitudinal reinforcement and the tensile force of the stirrup produce the diagonal compression in the sub strut.Theoretically predicted shear strengths of tested deep beams showed good agreement with experimentally observed shear strengths, where the effective strength of concrete was assumed to be 75% of the cylinder strength.

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The clamping force of a high-strength bolt reduces within a certain time period after the initial clamping force. When special treatments are used on a faying surface, the clamping force is relaxed severely. Tests were conducted for slip critical joints subjected to various faying surface parameters. Relaxation occurred for slip resistant joints with an uncoated surface that had been shot-blasted, cleaned, milled or rusted. It was observed that the initial clamping force dropped from 6.2% to 8.0% after 744 hours. For joints with a 5 mil thick zinc coating, the clamping force of the bolts decreased by 8.37%, and in the case of 4.9 mil thick red lead painted treatment, the relaxation ratio was 24.6%. The standard deviation of the slip coefficients between the time immediately after tightening and 1,000 hours after tightening was 0.223. It is particularly noteworthy that, for red lead painted treatment, the slip coefficient dropped from 2.5 times to 2.8 times when compared with the slip coefficient before relaxation. Joints with inorganic zinc should not have thickness exceeding 5 mils, and joints with a red lead painted surface should not be allowed regardless of the thickness of coating.