Semi-Rigid connections in composite structures

In this study, the behavior of intermediate semi-rigid composite extended end-plate connection is studied in details. A three dimensional finite element model IS developed taking into consideration the geometric non-linearity of the model. An experimental work is performed to check the validity of the proposed finite element model and to study the effect of some parameters on the connection behavior. Five connections scaled to the one third are tested experimentally and compared with their counterpart connections analyzed by the proposed finite element model.Comparison between experimental and numerical results showed that, the proposed finite element model simulates the semirigid composite connection of the type studied with a reasonable accuracy. where comparison between the moment-rotation curves from test and analysis showed that, the percentage of difference in the finite element results range between 5.30/0 to 7.7% in all connections, where the finite element analysis results under estimate the connection rotational stiffness. Comparison between the vertical deflection of the loading points obtained from both experimental work and analysis shows that, the percentage of difference in the finite element results range from 8.80/0 to 13% in all connections. Also, comparison between the pattern of the cracks propagation shows that, the cracks propagation obtained from test and analysis have the same trend ofpropagation but the difference is in the value of the load causing the same crack, as a result of the difference between the means of determination of the cracks in test and analysis.Based on the results obtained from the experimental work and within the range of the selected variables, the following conclusions can be deduced:(I) Presence of composite floor slab with only anti-crack steel mesh on the bare steel connection increases considerably the rotational stiffness of the connection. The composite connection has an initial rotational stiffness equals about 3.5 times that of the bare steel connection.(2) The additional upper steel reinforcement to the composite slab covering the area of negative bending moment with adequate anchorage length and distributed in a width equals the effective width of the compression flange, has a smal1 effect on the initial stiffness of the connection, because the effect of the additional steel starts after cracking of the concrete slab and allows the transmission of the tensile stresses from cracked concrete to the steel bars.(3) Composite connection with (0.67% Ac) additional steel reinforcement to the slab has a rotational stiffness equals about 3.70 times that of the bare steel connection.(4) Increasing the thickness of the connection end-plate from (8 mm to 10 mm), i.e., by about 250/0 increased the connection initial stiffness by about 300/0.(5) At failure, the connections loose most of their stiffness where the moment-rotation curves become approximately horizontal.