Behaviour and design of composite beams subjected to negative bending and compression

This paper investigates the behaviour of steel–concrete composite beams subjected to the combined effects of negative bending and axial compression. Six full-scale tests were conducted on composite beams subjected to negative moment while compression was applied simultaneously. Following the tests, a nonlinear finite element model was developed and calibrated against the experimental results. The model was found to be capable of predicting the nonlinear response and the ultimate failure modes of the tested beams. The developed finite element model was further used to carry out a series of parametric analyses on a range of composite sections commonly used in practice. It was found that, when a compressive load acts in the composite section, the negative moment capacity of a composite beam is significantly reduced and local buckling in the steel beam is more pronounced, compromising the ductility of the section. Rigid plastic analysis based on sectional equilibrium can reasonably predict the combined strength of a composite section and, thus, can be used conservatively in the design practice. Based on the experimental outcomes and the finite element analyses a simplified design model is proposed for use in engineering practice

3D numerical assessment of the progressive collapse resistance of a seismic-resistant steel building with post-tensioned beam-column connections

This paper presents the numerical assessment of the progressive collapse resistance of a seismic-resistant steel building with post-tensioned beam-column connections. The numerical simulations are carried out in 3D under a loss of column scenario. The 3D model considers the effect of the composite slab, where composite beams and their shear connectors are modeled with a combination of shell, beam and nonlinear connector elements. All the beam-column and beam-to-beam connections are modeled using nonlinear connector elements with appropriate failure criteria. Moreover, the steel frame for which a column is removed is modelled in full detail with the aid of 3D solid elements to accurately capture its local and global nonlinear behavior. Nonlinear static analyses are carried out to identify the failure modes of the building under a sudden loss of column scenario and investigate the effect of the floor slab on the overall progressive collapse resistance

Self-centering steel column base with metallic energy dissipation devices

Column bases of seismic-resistant steel frames are typically designed as full-strength to ensure that plastic hinges develop in the bottom end of the first-storey columns. Alternatively, column bases may be designed as partial-strength and dissipate energy through inelastic deformations in their main components (i.e., base plate, steel anchor rods). Both design philosophies result in difficult-to-repair damage and residual drifts. Moreover, the second design philosophy results in complex hysteretic behaviour with strength and stiffness deterioration. This paper proposes a partial-strength low-damage self-centering steel column base. The column base provides flexibility in the design as its rotational stiffness and moment resistance can be independently tuned. The paper presents an analytical model that predicts the stiffness, strength, and hysteretic behaviour of the column base. In addition, a design procedure and detailed finite element models are presented. The paper evaluates the effectiveness of the column base by carrying out nonlinear dynamic analyses on a prototype steel building designed as post-tensioned self-centering moment-resisting frame. The results demonstrate the potential of the column base to reduce the residual first-storey drifts and protect the first-storey columns from yielding.</p

Design and modeling of a novel damage-free steel column base

Column bases are fundamental components of a steel frame. However their design has not yet received appropriate attention. Conventional steel column bases cannot be easily repaired if damaged and exhibit difficult-to-predict and simulate stiffness, strength and hysteretic behaviour. This paper proposes a novel demountable and fully repairable column base for resilient steel buildings. The new column base isolates damage in easy-to-replace structural elements with the goal of minimizing repair time and disruption of the building service in the aftermath of a strong earthquake. Moreover, it can be easily constructed and deconstructed to enable sustainable steel frame designs. It provides significant flexibility in the design, with rotational stiffness and moment resistance that can be independently tuned. It has self-centering capability for reducing residual drifts. The paper presents design rules, an analytical hysteretic model and a 3D finite element model for the new column base

Progressive collapse resistance of steel self-centering MRFs including the effects of the composite floor

This paper presents progressive collapse simulations to assess the robustness of a seismic-resistant building using self-centering moment resisting frames (SC-MRFs) under a sudden column loss scenario. The first floor of the building, including the composite floor, was modelled in ABAQUS using a mixture of finite element types and simulation methods to balance computational cost and accuracy. First, key components of the numerical model, including the composite beams, the fin-plate beam-column connections, and the perimeter SC-MRFs, were validated against available experimental results to ensure a reliable simulation. The validated model was then used to study the robustness of the building under a sudden column loss event. Both nonlinear static and dynamic analyses were employed. The simulations allowed for the identification of all possible failure modes and the quantification of the contribution of the composite floor to the robustness of the frame. The results show that the building can withstand the code-prescribed load with a safety factor of 2 and that the structural limit state that triggers progressive collapse is the buckling of the gravity columns. The Dynamic Increase Factor (DIF) was also identified by comparing the static and dynamic responses

Shear strength and moment-shear interaction of steel-concrete composite beams:Experiments, numerical analyses, and design models

Current structural codes do not address the shear strength and the moment-shear interaction in composite beams explicitly. The shear is commonly assumed to be resisted by the steel beam alone neglecting the contributions of the slab and the composite action. This paper presents an experimental and numerical study to cover this gap. Fourteen composite beams and one steel beam were tested in order to investigate the contribution of the concrete slab to the shear strength of a composite section and the moment-shear interaction in compact composite beams. A nonlinear finite element model was also developed to complement the experimental results. It was found that the moment capacity of a composite beam is significantly reduced when high shear forces are present. The reduction in moment capacity is accompanied by failure modes consisting of web buckling in the steel beam and brittle shear failures in the concrete slab, while the ductility is largely compromised. A significant contribution of the concrete slab to .the shear capacity of the composite section was determined by the tests and verified by the numerical analyses. Based on the experimental and numerical results design models are proposed for the robust and economical design of compact composite beams under high shear forces, and for incorporation into design standards