Search

The monotonic behavior of externally post-tensioned steel–concrete composite girders was numerically studied in this paper. A three-dimensional numerical model was developed and validated using experimental test results that were conducted by the authors and using an existing analytical model. A parametric study using this validated numerical model was performed to investigate the effects of various parameters on the monotonic performance of composite girders strengthened with external post-tensioned tendons. The parameters investigated include variations in the degree of shear connection, layout and diameter of shear connectors, the initial post-tensioning force, the depth of the steel beam, the eccentricity of the tendons, the compressive strength of concrete, and the shear capacity of the studs. The numerical model provided a better understanding of the effect of these parameters on the behavior of the strengthened beams. The results of the parametric study show that as the degree of shear connection decreased, the stud strains increased and the slippage between the concrete deck and steel beam increased. As the full degree of shear connection was reduced to 80%, 60%, and 40%, the stud strains were increased by 20%, 46%, and 94%, respectively. Also, as the shear connection degree decreases, its effect on the slippage behavior increases. As the degree of shear connection was reduced to 80%, 60%, and 40%, the slippage values were increased by 23%, 48%, and 102%, respectively. The study also shows that, for the same degree of shear connection, beams with one row of shear studs had up to 10% higher flexural capacity than beams with two rows of studs. A 100% increase in the stud diameter caused a 28% reduction in the ultimate load capacity and a 160% increase in the maximum slippage. The higher the post-tensioning force, the higher the ultimate load capacity and the lower the tensile strains in the steel beam. A 118% increase in the post-tensioning force resulted in a 9% increase in the ultimate load capacity and a 13% reduction in the tensile strains. Increasing the depth of the steel beam by 40% resulted in a reduction in the tensile strains at midspan by 20%. The lowest midspan tensile strains were obtained from the combination of increasing the depth of the steel beam and tendon eccentricity.

The use of cold-formed steel trusses in roof framing has significantly increased recently. Cold-formed steel roof trusses are ideal and efficient systems for a variety of applications due to their design flexibility and ease of construction. Past research explored the behavior of these truss systems up to the ultimate capacity point; however, the inelastic behavior to the failure was not fully captured. Information about the response beyond the buckling point and the energy absorption capacities are missing and need to be investigated. In this paper, small-scale cold-formed steel roof truss specimens were tested to failure under quasi-static loading. The static resistance of these systems and the associated failure mechanisms were identified. Such information is key input when analyzing these roof systems under blast loads using the Single Degree of Freedom simplified technique. Experimental results and absorbed energy comparisons show that the truss layout and the shape of loading significantly affect the performance of the truss and the failure mechanism. Three-dimensional finite element models were developed and verified against the experimental results. The advanced models predicted the static resistance with a high level of accuracy. Experimental and finite element analyses have shown that the energy absorbed is improved significantly when the web members susceptible to buckling are strengthened.

In bolted composite connections design, staggered arrangements might offer a good area usage especially for structural elements with a small width. In this research, experimental and numerical works were employed to study the composite-steel double lapped joints with staggered bolts arrangement under static loads. Staggered bolt arrangement was studied with different bolt diameters and numbers. The predictions of developed models were compared to the experimental results and a good correlation was evaluated. The experimental study shows that the side distance in the staggered bolted joint has a significant influence on the maximum load due to the out-of-plane rotation. Simulation of the experimental work shows that this out-of-plane rotation produces a horizontal force on the direction causing early failure for the joint. A parametric study was performed to investigate the effect of bolt numbers and diameters. It was found that the number of bolts has a more significant effect on increasing joint failure load than the bolt diameter. In all cases, the first bolt from the composite plate side has the maximum force, therefore, the first damage happened under this bolt. Considering the axial applied load direction as a reference direction, high perpendicular to parallel forces ratio was evaluated on the bolts of the staggered joint. It is recommended to consider this force during the design of the laminate. Furthermore, the staggered bolt arrangement was found to cause a significant out-of-plane bending which is recommended to be taken into consideration.

The nonlinear responses of guyed towers under static loads and under dynamic loads are investigated by using the developed nonlinear Finite Element Method (FEM). Through the use of the developed fully nonlinear element formulations for structural components such as trusses, cables, and beams, it is possible to capture the complete geometric nonlinear response with the assistance of iterative algorithms such as Crisfield’s method and the Newmark beta method. One 50 ft high guyed tower subjected to a constant top-concentrated load and one 328 ft guyed tower subjected to an EI Centro earthquake are used as demonstration. The results of the static analysis are compared with the results from SAP2000, ANSYS, and a linear equivalent column method. The results of the SAP2000, ANSYS, and the developed nonlinear FEM algorithm match well when the deflection is relatively small. In the Linear Equivalent Method, the equivalent spring-supported beam method provides the most accurate estimation when the deflection is relatively small. The complete time history of the guyed tower is also obtained for the nonlinear dynamic analysis.

The direct design method recommended by ACI is commonly used for the design of flat slabs. Since the flexural stiffness of the waffle slab varies along the span, it is expected that the distribution of moments is different from that of flat slabs. Current design procedures do not provide recommendations specific of waffle slabs. Designers smear the contribution of the ribs and use the design guidelines for flat slabs to design ribbed slabs. In addition, the effect of openings on the response of waffle slabs is not fully explored. Therefore, modified moment coefficients are needed for waffle slabs. In this paper, numerical simulations using ANSYS are used to study the response of waffle slabs with and without openings. The main objectives of this paper are: (1) to obtain the design coefficients for the column and the field strips of the internal panel of a waffle slab and (2) to study the effect of openings and stiffening ribs on the design coefficients. Ninety Linear and non-linear analysis models using ANSYS were performed in the study to evaluate the response of various waffle slabs under uniform loading. The main parameters evaluated are the column size, the solid portion size, the opening size and its location, and the effect of stiffener ribs around the opening. The non-linear finite element model was verified using existing experimental results for two waffle slabs. The moment coefficients developed in this paper were used to modify the existing ACI flat-slab coefficients to be used for waffle slabs.