A new damage index for plane steel frames exhibiting strength and stiffness degradation under seismic motion

A new damage index for plane steel frames under earthquake ground motion is proposed. This index is defined at a section of a steel member and takes into account the interaction between the axial force N and bending moment M acting there. This interaction is defined by two curves in the N-. M plane. The first curve is the limit between elastic and inelastic material behavior, where damage is zero, while the second one is the limit between inelastic behavior and complete failure, where damage is equal to one. The damage index is defined by assuming a linear variation of damage between the two abovementioned curves. Thus, for a given N-. M combination at a member section, obtained with the aid of a two dimensional finite element program, one easily defines the damage index of that section. Material nonlinearities are taken into account by a stress-strain bilinear model including cyclic strength and stiffness degradation in the framework of lumped plasticity (plastic hinge model), while geometrical nonlinearities are modeled by including large deflection effects. The increase of damage related to strength reduction due to low-cycle fatigue is also taken into account. Several illustrative examples serve to demonstrate the use of the proposed damage index and to compare it with other well known damage indices. © 2012

Seismic design of space steel frames using advanced static inelastic (pushover) analysis

A rational and efficient seismic design method for regular space steel frames using inelastic (pushover) analysis (PA) is presented. This method employs an advanced static finite element analysis that takes into account geometrical and material non-linearities and member and frame imperfections. Resistances (strengths) are computed according to Eurocodes 3. The PA is employed with multimodal lateral loads along the height of the building combining the first few modes. The design starts with assumed member sections, continues with deformation and damage check at three performance levels with the aid of PAs and ends with the adjustment of member sizes. Thus, it can sufficiently capture the limit states of displacements, strength, stability and damage of the structure and its individual members so that separate member capacity checks through the interaction equations of Eurocode 3 or the use of the behavior factor q suggested in Eurocode 8 are not required. One numerical example dealing with the seismic design of a one bay in both horizontal directions and three storey steel moment resisting frame is presented to illustrate the method and demonstrate its advantages. © 2020 Elsevier Lt

Seismic collapse of self-centering steel MRFs with different column base structural properties

The effect of the strength and stiffness characteristics of a previously proposed novel column base on the seismic performance and collapse capacity of steel self-centering moment-resisting frames is evaluated in this paper. This is done through three normalised parameters that represent the initial stiffness, post-yield stiffness, and strength of the column base, which can be independently adjusted. For these evaluations, a prototype steel building, which serves as a case study, is designed with sixteen different cases of a self-centering moment-resisting frame with different column base stiffness and strength characteristics (SC-MRF-CBs). A self-centering moment-resisting frame with conventional column bases and the same members and beam-column connections as those of the SC-MRF-CBs, named SC-MRF, serves as a benchmark frame. A set of 44 ground motions was used to conduct non-linear dynamic analyses and evaluate the seismic performance of the frames. Incremental dynamic analyses were also performed with the same ground motions set to evaluate the collapse capacity of the frames. Collapse capacity fragility curves and adjusted collapse margin ratios of the frames were derived and used for the comparison of the seismic risk of the frames. The results show that the new self-centering column base significantly improves the seismic performance of the SC-MRF, demonstrating the potential of the SC-MRF-CBs to be redesigned with smaller member sections. Moreover, the SC-MRF-CBs achieve significant reduction in collapse risk compared to the SC-MRF. Finally, the results show that increasing the base strength and stiffness improves the seismic performance and collapse capacity of the SC-MRF-CBs. © 2020 Elsevier Lt

Direct damage-controlled design of plane steel moment-resisting frames using static inelastic analysis

A new direct damage-controlled design method for plane steel frames under static loading is presented. Seismic loading can be handled statically in the framework of a push-over analysis. This method, in contrast to existing steel design methods, is capable of directly controlling damage, both local and global, by incorporating continuum damage mechanics for ductile materials in the analysis. The design process is accomplished with the aid of a two-dimensional finite element program, which takes into account material and geometric nonlinearities by using a nonlinear stress-strain relation through the beam-column fiber modeling and including P-δ and P-Δ effects, respectively. Simple expressions relating damage to the plastic hinge rotation of member sections and the interstorey drift ratio for three performance limit states are derived by conducting extensive parametric studies involving plane steel moment-resisting frames under static loading. Thus, a quantitative damage scale for design purposes is established. Using the proposed design method one can either determine damage for a given structure and loading, or dimension a structure for a target damage and given loading, or determine the maximum loading for a given structure and a target damage level. Several numerical examples serve to illustrate the proposed design method and demonstrate its advantages in practical applications

Residual drift risk of self-centering steel MRFs with novel steel column bases in near-fault regions

This paper evaluates the potential of novel steel column bases to reduce the residual drift risk of steel buildings located at near-fault regions when installed to post-tensioned self-centering moment-resisting frames (SC-MRFs). To this end, a prototype steel building is designed that consists of either conventional moment-resisting frames (MRFs) or SC-MRFs or SC-MRFs equipped with the novel steel column base (SC-MRF-CBs). The MRFs and SC-MRFs are used as benchmark frames. The frames are modelled in OpenSees where material and geometrical non-linearities are considered along with stiffness and strength degradation. A set of 91 near-fault ground motions with different pulse periods is used to perform incremental dynamic analysis (IDA), in which each ground motion is scaled appropriately until different residual storey drift limits are exceeded. The probability of exceedance of these limits is then computed as a function of the ground motion intensity and the period of the velocity pulse. Finally, the results of IDA are combined with probabilistic seismic hazard analysis models that account for near-fault directivity to evaluate and compare the residual drift risk of the frames used in this study. Results show that the predicted residual drift performance of the frames is influenced by the pulse period of the near-fault ground motions. The use of the novel steel column base significantly reduces the residual drift risk of the frames and the SC-MRF-CB exhibits the best residual drift performance. Finally, the paper highlights the effectiveness of combining post-tensioned beam-column connections with the novel steel column base, by showing that the SC-MRF-CB improves the residual drift performance of the MRF and SC-MRF by 80% and 50%, respectively

Flexural buckling behaviour of concrete-filled double skin aluminium alloy columns

Concrete-filled double skin steel tubular columns consisting of two hollow steel tubes and concrete infill between their interspace, have become popular in modern construction owing to their high ultimate load, less self-weight and good ductility. The weight of these columns can be reduced further by using lightweight aluminium alloy hollow tubes instead of steel ones. This paper experimentally and numerically studied the flexural buckling behaviour of the concrete-filled double skin aluminium tubular (CFDSAT) columns subjected to axial compression. A total of 8 CFDSAT columns were tested using a pin-ended set-up. The test results are presented in terms of failure modes, ultimate load and load versus mid-height lateral displacement curves. Non-linear finite element (FE) models of the specimens were developed and their accuracy was evaluated by comparing the FE and test results. A numerical parametric investigation was conducted to study the influence of the hollow ratio, the member slenderness, the cross-sectional slenderness of the hollow tubes and the concrete strength on the structural behaviour of CFDSAT columns. The parametric study results revealed that the cross-sectional dimensions of outer section, the member slenderness and the concrete compressive strength have a significant effect on the flexural buckling response of the columns, while the influence of the cross-sectional dimensions of inner section is less prominent. In the absence of design standards for CFDSAT members, a design methodology is proposed with a design buckling curve to predict the ultimate load of CFDSAT columns based on the Eurocode 4 framework. Moreover, a revised concrete correction factor is suggested to determine the effective flexural rigidity of CFDSAT columns according to Eurocode 4

Experimental and numerical investigation of the earthquake response of crane bridges

© 2014 Elsevier Ltd. The experimental and numerical response of crane bridges is studied in this work. To this end, an experimental campaign on a scale model of an overhead crane bridge was carried out on the shaking table of CEA/Saclay in France. A special similarity law has been used which preserves the ratios of seismic forces to friction forces and of seismic forces to gravity forces, without added masses. A numerical model, composed of beam elements, which takes into account non-linear effects, especially impact and friction, and simulates the earthquake response of the crane bridge, is presented. The comparison of experimental and analytical results gives an overall satisfactory agreement. Finally, a simplified model of the crane bridge, with only a few degrees of freedom is proposed

Design of aluminium alloy channel sections under minor axis bending

In recent years, numerous research works have been reported on the flexural response of aluminium alloy tubular cross-sections. However, studies on monosymmetric cross-sections and particularly channel (C-) sections are limited, albeit their increased usage in structural applications. This paper aims to address this knowledge gap providing an improved understanding about the minor axis bending behaviour of C-sections through an experimental and numerical investigation. In total 14 specimens made from 6082-T6 heat-treated aluminium alloy were subjected to four-point bending. Tensile coupon tests were also performed to determine the mechanical properties of the examined aluminium alloy. The obtained experimental results are analysed and discussed. A series of geometrically and materially nonlinear analyses were also carried out to study the flexural performance of C-sections in two aluminium alloys and two bending orientations over a range of cross-sectional aspect ratios and slendernesses. The experimental and numerical results are utilised to assess the European design standards. The applicability of the Continuous Strength Method and the Direct Strength Method is also evaluated. An alternative design method based on the plastic effective width concept is proposed for slender C-sections subjected to minor axis bending. This method accounts for the inelastic reserve capacity which is in accordance with the experimental and numerical observations

Ultimate response and plastic design of aluminium alloy continuous beams

Over the last twenty years 6,000 series aluminium alloys are gaining increasing attention as a structural material in the construction sector, particularly in applications where lightness and corrosion resistance are crucial for material selection. Aiming to sustainable construction practices, significant material savings could be achieved through more economical design solutions such as plastic design. Currently, plastic design of aluminium alloy structures is not permitted in most design codes, except European provisions which provide recommendations for inelastic analysis. Indeed, there is a clear lack of experimental data to prove this possibility, particularly for relatively new materials in the construction industry, such as the 6082-Τ6 heat-treated aluminium alloy. To address this knowledge gap, a total of 15 rectangular hollow sections fabricated from 6082-T6 aluminium alloy were tested as simply-supported and two-span continuous beams. Numerical models were developed to replicate the experimental results considering geometric and material nonlinearities. A subsequent parametric study was carried out to generate numerical data for indeterminate structures. One normal and two high strength aluminium alloys as well as two load configurations were examined within this parametric study over a wide range of cross-sectional aspect ratios and slendernesses. The experimental results in combination with the numerical results were utilised to assess the accuracy and applicability of (i) the traditional plastic design method, (ii) the European design provisions (EC9), (iii) the plastic hinge method included in Annex H of EC9, and (iv) the Continuous Strength Method (CSM). Relative comparisons demonstrated the potential of applying plastic design in aluminium alloy indeterminate structures. Notably, the plastic hinge method and the CSM which accounts for strain hardening at the cross-sectional level and for moment redistribution at the system level were found to provide the most accurate design strength predictions, resulting in more economical cross-sections and utilising the full potential of aluminium alloys’ plastic deformability