AbstractNonlinear static and dynamic analyses are utilized by engineers for performance-based seismic risk evaluation of new and existing structures. In this context, nonlinear component modeling ...criteria are typically based on ASCE 41 guidelines. Experiments on wide-flange steel columns suggest that the ASCE 41-13 nonlinear component models do not adequately reflect the expected steel column behavior under cyclic loading. To help bridge the gap between state-of-the-art research and engineering practice, this paper proposes new modeling criteria for the first-cycle envelope and monotonic backbone curves of steel wide-flange columns for use in nonlinear static and dynamic frame analyses. The proposed nonlinear provisions include new parameters for concentrated hinge models to facilitate modeling of strength and stiffness deterioration of steel columns under seismic loading. The associated variability in the model parameters is also quantified to facilitate reliability analyses and development of probabilistic acceptance criteria for design. Recommendations are made to account for the influence of bidirectional lateral loading and varying axial load demands on the steel column’s hysteretic behavior. Also proposed is an increase in the compression axial force limit for characterizing columns as force-controlled versus deformation-controlled in line with the new ASCE 41 provisions. The proposed modeling parameters are validated against test data and continuum finite-element analyses, and they are proposed for consideration in future updates to ASCE 41 requirements for nonlinear static and dynamic analyses of steel frame buildings with wide-flange columns.
A new type of the strengthened strategy for the limited anti-collapse capacity of extended end-plate connections (EEC) is proposed. Bending stiffened steel plates (BSSPs) were placed in the joint ...region to form a new type of strengthened extended end-plate connection (SEEC). BSSPs are beneficial to improve the robustness of EECs against progressive collapse.
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•A new type of strengthened extended end-plate connection (SEEC) is proposed.•The geometric motion characteristics of the bending stiffened steel plates (BSSPs) are described through theoretical analyses.•The process of resistance development in the SEEC comprises three stages: elastic, transition, and improvement.•SEEC can obtain a more significant improvement stage.•SEEC design process is given.
In this paper, a new type of the strengthened strategy for the limited anti-collapse capacity of extended end-plate connections (EECs) is proposed. Bending stiffened steel plates (BSSPs) were placed in the joint region to form a new type of strengthened extended end-plate connection (SEEC). First, the geometric motion characteristics of the BSSPs on the tensile and compression sides of the joint are described through theoretical analyses, and the improvement mechanism of the anti-collapse performance of the SEEC is given. Subsequently, using the verified numerical model, nine groups of parameters affecting the ultimate rotation of the EEC were analyzed, and the calculation formula for the ultimate rotation of the EEC was given via nonlinear fitting based on its numerical results. The numerical analysis example shows that the process of resistance development in the SEEC comprises three stages: elastic, transition, and improvement. Among them, the BSSP works well with bolts and end plate, which makes the SEEC obtain a more significant improvement stage and proves that the BSSP design process is reasonable. Finally, the main parameters a1, b1, and the thickness of the SEEC, were analyzed and suggested using parametric analysis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Four types of seismic moment connections tested under column loss scenario.•Two full strength connections and two partial strength connections.•Finite element models validated against experimental ...data.•Three connections experienced large deflections prior to failure.•Partial strength connection requires strengthening to improve deformation capacity.
The beam-to-column connections of moment-resisting steel frames should exhibit capacities that allow them to transfer the forces that develop under normally expected loading conditions. However, when a column is lost owing to accidental loading, these conditions change, and the forces are redistributed to the adjacent beams and columns. In such cases, the connections must be capable of resisting the combined axial and flexural loads and allow for the redistribution of the loads, so that progressive collapse development is prevented. In this study, we investigated the performances of four types of beam-to-column connections, namely, the welded cover plate flange connection (CWP), the haunch end plate bolted connection (EPH), the reduced beam section welded connection (RBS), and the unstiffened extended end plate bolted connection (EP), against progressive collapse. Two span frames were constructed and tested under a central column removal scenario until failure. The results from the experimental tests were used to validate finite element models. The CWP, EPH, and RBS specimens showed good ductility, with the catenary action making a significant contribution to the ultimate load resistance. Further, the ultimate rotations of the beams were greater than the deformation limit given in the latest Unified Facilities Criteria guidelines for design of buildings to resist progressive collapse. Specimen EP showed the lowest ductility and ultimate load resistance, with the bolts in the rows under tension fracturing before the catenary action could develop. Further, the failure mode for specimen EP indicated that bolt strengthening is necessary for improving its progressive collapse resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A dual seismic-resistant steel frame, which consists of a moment-resisting frame equipped with high post-yield stiffness energy-dissipative braces, is proposed and numerically evaluated. Replaceable ...hourglass shape pins made of duplex stainless steel with high post-yield stiffness and large energy dissipation and fracture capacity are in series connected to conventional steel braces. Moreover, replaceable fuses are introduced in the beams at the locations where plastic hinges are expected to develop. A performance-based seismic design procedure and appropriate capacity design rules are used to design the dual frame, while its seismic performance is evaluated with advanced numerical simulations using experimentally validated shell–solid finite element models and simplified beam element models. The numerical results show that the dual frame has adequate stiffness and energy dissipation capacity to control peak storey drifts (i.e. non-structural damage), while plastic deformations (i.e. structural damage) are isolated within the replaceable pins of the braces and the beam fuses. In addition, the high post-yield stiffness of the pins, combined with the appreciable elastic deformation capacity of the moment-resisting frame, results in significant reduction of residual storey drifts, which are found to have a mean value of 0.06% under the design earthquake and a mean value of 0.12% under the maximum considered earthquake. These values indicate a superior residual storey drift performance compared to steel frames equipped with buckling restrained braces, and highlight the potential of the proposed dual frame to help steel buildings to return to service within an acceptable short time in the aftermath of a strong earthquake.
•A novel dual seismic-resistant steel frame for drift reduction is proposed.•Braces are equipped with stainless steel pins with high post-yield stiffness.•Stiffness and strength comparable with conventional steel systems•Advanced numerical models show a superior residual storey drift performance.•Structural and non-structural damage are drastically reduced.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A novel type of steel column equipped with NiTi SMA bolts was proposed for earthquake resilience.•An analytical model of the SC column for various limit states and a design procedure were ...presented.•Experimental investigations on the SC columns with representative parameters were carried out.•The analytical model was verified through a comparison with test results.
Steel moment-resisting frames are popular structural systems used extensively around the world. However, conventional column base connections are vulnerable to large residual deformation after strong earthquakes. By contrast, shape memory alloys (SMAs), which are high-performance metallic materials, can experience large strains and still recover their initial shape through either heating (shape memory effect) or unloading (superelastic effect). The superelastic behavior of SMAs is appealing to the earthquake engineering community because of the material’s excellent self-centering (SC) and energy dissipation capabilities. In this paper, a novel type of steel columns equipped with NiTi SMA bolts was introduced and its potential for achieving earthquake resilience were investigated. Structural details of the column base and mechanical properties of the SMA bolts were described first. Subsequently, an analytical model of the SC column for different limit states and the corresponding design procedure were presented. The seismic behaviors of two steel column specimens were experimentally tested to investigate the effects of the initial prestrain in the SMA bolts and the axial compressive force in the column under cyclic loading. Results showed that the steel columns equipped with SMA bolts exhibited satisfactory and stable flag-shaped hysteresis loops with excellent SC and moderate energy dissipation capabilities. More importantly, SMA bolts with prestrain could still be tightened after removal of lateral force. Therefore, the proposed SC column could achieve seismic resilience design that requires no (or minimal) repair even after strong earthquakes and remains highly functional for aftershocks or future earthquakes. In addition, the analytical model was verified through a comparison with test results obtained at key limit states.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
AbstractShake-table tests, subjected to mainshock–aftershock sequences, were conducted on a 1/3-scaled 3-story steel frame equipped with self-centering viscous-hysteretic devices (SC-VHDs) and its ...primary frame to investigate the effect of the aftershock on seismic performance. It was found that the SC-VHD can effectively reduce 30%–50% of the peak drift and 50%–80% of the residual drift, respectively. Additionally, the peak and residual drifts of the 3-story primary frame under the mainshock–aftershock sequences were more than those under the mainshock-only sequences, while the peak and residual drifts of the 3-story SC-VHD frame under the mainshock-only and mainshock–aftershock sequences were basically the same. A numerical simulation method for the SC-VHD frame was further developed and validated, based on which 6-, 9-, and 12-story SC-VHD frames were analyzed to investigate the seismic performance of medium- high-rise SC-VHD frames. Both shake-table tests and numerical analysis indicate that the peak and residual drifts of the 3-, 6-, 9-, and 12-story SC-VHD frames can meet the design objective under the mainshock–aftershock sequences.
Initial geometric imperfections are unavoidable in steel members and frames due to erection and manufacturing tolerances. These include frame out-of-plumbness, member out-of-straightness and ...cross-sectional imperfections, and can have a significant influence on the response and resistance of steel structures. Thus, they need to be accounted for in the analysis and design of steel structures, especially when advanced design procedures are adopted. One of the easiest approaches to introduce geometric imperfections in structural finite element models is through the linear superposition of scaled eigenmodes, which are obtained from a priori elastic buckling analysis. Although the shape and magnitude of frame and member imperfections are specified in international standards, the rules for the combination of different types and directions of imperfections are unclear or impractical, and often require designers to consider many possible combinations to find the critical, or “worst case”, shape of the imperfection including the direction of each eigenmode. This paper investigates the influence of the direction of modes contributing to the imperfection on the ultimate load (i.e., resistance) of steel frames when using advanced analysis. Ultimate loads are estimated from advanced finite element simulations for 20 regular and irregular unbraced frames featuring steel and austenitic stainless steel compact sections, in which initial imperfections are modelled as linear superpositions of six scaled buckling modes considering all possible combinations of direction. The results show that the influence of the imperfection direction on the ultimate frame load is small, and that assuming a combination of all buckling modes with positive amplitudes provides a simple and accurate estimation of the critical imperfection combination.
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•Influence of the imperfection direction on the strength of steel frames is investigated.•Imperfections are modelled as a linear superposition of six scaled buckling modes.•Different regular and irregular steel and stainless steel frames with compact sections are examined.•Ultimate load factors for all possible direction combinations are obtained and compared.•The notion of worst case imperfection is challenged.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The hybrid steel frame is a new laterally resistant steel frame composed of rigid and semi-rigid connections. The objective of this study is to select a hybrid frame with an appropriate seismic ...performance based on a multi-criteria decision-making approach. The seismic performance of different patterns and positions of semi-rigid connections within the selected frames is examined. Static, cyclic and nonlinear dynamic analyses are conducted on the selected frames. The Analytic Hierarchy Process is then used to evaluate the performance of the frames. The results indicate that the hybrid frame can offer an enhanced performance in comparison with rigid frames if the hybrid frame is well proportioned.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
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