Design Of Steel Moment Resisting Frames Research Articles

Optimum seismic design of frame structures with and without metallic yielding dampers considering life-cycle cost

This paper investigates the optimal design of steel moment-resisting frame (MRF) buildings, with and without metallic yielding dampers, using a life-cycle cost (LCC)-based optimal design process. The aim is to minimize the LCC as the design criterion, which includes construction cost and the loss of lifetime seismic consequences. The study employs the endurance time (ET) method for structural response analysis and the FEMA P-58 procedure for seismic loss assessment. Four design approaches are examined: (1) typical code-based design of an existing MRF without damper, (2) optimal LCC-based design of a new MRF without damper, (3) optimal LCC-based design of an existing MRF equipped with damper, and (4) optimal LCC-based design of a new MRF equipped with damper. In the third scenario, only the damper properties are optimized, whereas in the fourth scenario, both the frame and damper properties are optimized together. The main contribution of this study is the simultaneous comparison of the design outcomes from the four aforementioned design approaches. The results indicate that LCC-based re-designed structures can effectively reduce costs compared to code-based designs. The best results were achieved by incorporating metallic dampers. Moreover, incorporating dampers also reduced the construction cost for the LCC-based re-designed cases. Based on the results, when dealing with similar scenarios, adding dampers to an existing frame can be sufficient, eliminating the need to redesign both the damper and frame together.

Optimum displacement profile for the direct displacement-based design of steel moment-resisting frames

The direct displacement-based design (DDBD) procedure is well established for designing reinforced concrete and steel moment-resisting frames (SMRFs). However, a limited number of researches is available on optimum DDBD of SMRFs. Furthermore, the nonlinear time-history analysis response of structures designed based on this procedure is inconsistent with its initial assumptions. Design displacement profile is one of the most essential and influential parameters in the DDBD method because it can impress other design parameters. In this paper, an optimum displacement profile is proposed to improve the results of the DDBD procedure via using the particle swarm optimization (PSO) algorithm. In this regard, nine SMRFs with a different number of stories have been designed using the DDBD procedure. Nonlinear time history analyses are performed for these frames using OpenSees software. The models are subjected to a set of 20 ground motion records. Then, PSO algorithm has been used to optimize the displacement profile of the DDBD procedure to achieve uniform drift distribution along with the height of the frames. Finally, based on regression analysis, the optimum design displacement profile for SMRFs with a different number of stories is formulated. The proposed equations show an average reduction of about 20% and 40% in steel usage and design base shear of the frames, respectively, while they have uniform drift along their heights.

Eurocode 8 revision – Implications on the design and performance of steel moment-resisting frames: Case study

Since the 2004 release of the European seismic code – Eurocode 8, various improvements have been proposed to its rules. The standard is being revised and, in its current revised state, it has been restructured and expanded in content. The revisions related to steel structures and especially to the design of steel moment-resisting frames (SMRFs) are notable. Modifications in the definition of the ductility classes, grade-dependent material randomness factors, behaviour factors, inter-storey drift sensitivity index (θ), the local hierarchy criteria, and the design rules for the dissipative ductility classes (DC2 & DC3) are a few of the notable proposed changes. This paper aims to study and compare seismic designs and performances of SMRFs using the revised specific rules for steel design. To this end, a parametric case study, consisting of 96 frames, is devised by varying the key parameters such that the effects of the recent changes can be highlighted. The parameters varied are the design code, ductility classes, number of storeys, span length, and material strength. The case study frames are analysed and designed to both versions of the EC8. Later, the seismic performance of the case study SMRFs designed to the current and revised EC8 provisions are investigated through non-linear static and dynamic analyses using OpenSees. Additionally, the significance of two distinct joint modelling techniques is explored.The results show that stability is not the governing requirement with the revised code. Lighter solutions in terms of steel mass were possible for the regularly spaced frames using the revised code. It was noted, however, that contrary to the design intent and despite the higher behaviour factor used in DC3 & DCH frames, their solutions were not found to be lighter than those designed to DC2 & DCM in both code versions. The actual behaviour factors estimated from non-linear analyses were also found to be different from those used in design by a considerable margin. The over-strength component of the behaviour factor varied significantly between frames of different steel grades and ductility classes. It was observed that the component plays such a significant role in the overall behaviour factor that assigning a constant value may result in misleading estimates. The dynamic analyses results showed that the frames designed to both versions of EC8 demonstrated acceptable performance even at the near collapse limit state.

Multi-objective optimal design of steel MRF buildings based on life-cycle cost using a swift algorithm

This paper proposed a swift multi-objective optimization algorithm for the performance-based design of steel moment-resisting frame (MRF) buildings considering life-cycle cost (LCC). Two components of the life-cycle cost, including the initial construction cost and the lifetime seismic damage cost of the building, are considered as two separate objectives of the optimization problem and are minimized simultaneously using the proposed algorithm. The proposed algorithm called Multi-objective Uniform Damage Optimization (MUDO) is an adaptive method that utilizes the concept of uniform damage (deformation) theory. MUDO leads to design alternatives for the building that are optimal (minimum) for both mentioned objectives. These alternatives, called Pareto optimal designs, allow decision-makers to choose the optimal investment option according to the project goals and by the trade-off between optimization objectives. The proposed algorithm is used to optimize three steel MRF buildings with 3, 6, and 9 stories. The lifetime seismic damage cost is calculated by assessing seismic losses at several ground motion intensities and using a probabilistic approach presented in HAZUS. A Monte Carlo analysis is used in this research to account for inherent uncertainties in structural response. The results demonstrate that MUDO can find competitive Pareto optimal designs in a much shorter time compared to a well-known metaheuristic algorithm called non-dominated sorting genetic algorithm II (NSGA-II).

Proposed Panel Zone Model for Seismic Design of Steel Moment-Resisting Frames

AbstractThis paper proposes a new mechanics-based model for the seismic design of beam-to-column panel zone joints in steel moment-resisting frames. The model is based on realistic shear stress dis...

The application of endurance time method for optimum seismic design of steel moment-resisting frames using the uniform deformation theory

The application of endurance time method for optimum seismic design of steel moment-resisting frames using the uniform deformation theory

Multi-level Response Modification Factor Estimation for Steel Moment-Resisting Frames Using Endurance-Time Method

ABSTRACT The computational complexity and high computational costs are the main obstacles to estimate the seismic demand and capacity of non-linear structural systems and assess their seismic performance under strong earthquake events. On the other hand, the current response modification factors for seismic design of structures are mainly based on a single performance target, and therefore, cannot be directly used in modern performance-based design procedures. In this study, a low computational cost method is adopted for seismic performance assessment of steel moment-resisting frames and development of multi-level modification factors by using the newly-developed Endurance-Time method. The efficiency of the proposed method is demonstrated for 3, 5, and 7-storey frame examples. It is shown that compared to conventional methods using time-history and pushover analysis techniques, the proposed approach can significantly (up to 80%) reduce the computational costs. The results indicate that push-over analyses may lead to inaccurate results, while a good agreement is generally observed between the seismic demands predicted by Endurance-Time and Time-History methods (less than 10% error). The results of Endurance-Time method are then used to develop multi-level response modification factors for steel moment-resisting frames by taking into account the effects of earthquake intensity and the target performance level. It is shown that Endurance-Time method can accurately estimate the response modification factors and the corresponding earthquake intensity levels with significantly less computational cost compared to the conventional methods using incremental dynamic analysis. The proposed multi-level response modification factors should prove useful in performance-based seismic design of steel moment-resisting frames.

Seismic Design of Steel Moment-Resisting Frames with Damping Systems in Accordance with KBC 2016

An efficient design procedure for building structures with damping systems is proposed using nonlinear response history analysis permitted in the revised Korean building code, KBC 2016. The goal of the proposed procedure is to design structures with damping systems complying with design requirements of KBC 2016 that do not specify a detailed design method. The proposed design procedure utilizes response reduction factor obtained by a limited number of nonlinear response history analyses of the seismic-force-resisting system with incremental damping ratio substituting damping devices. Design parameters of damping device are determined taking into account structural period change due to stiffness added by damping devices. Two design examples for three-story and six-story steel moment frames with metallic yielding dampers and viscoelastic dampers, respectively, shows that the proposed design procedure can produce design results complying with KBC 2016 without time-consuming iterative computation, predict seismic response accurately, and save structural material effectively.

A more rational selection of the behaviour factor for seismic design according to Eurocode 8

The main objective of the research presented in this paper is to assess the influence of a more rational selection of the behaviour factor (q) for the seismic design of steel moment-resisting frames (MRFs) according to Eurocode 8 (EC8). To this end, a large set of steel MRFs were designed using for code-prescribed behaviour factors as well as using the Improved Force-Based Design (IFBD) methodology for a more consistent selection of q. The seismic performance of the archetypes was assessed through nonlinear static and response-history analysis. The results point to the discrepancy between the design assumptions and the real response of the structures, as significant differences between the design base shear and the lateral strength of the frames were observed for frames designed with code-prescribed behaviour factors. Moreover, it is shown that IFBD-designed steel frames exhibit more uniform inelastic demands over the building height, as well as ductility demands more compatible with the design assumptions. Finally, the fragility and seismic risk assessment conducted shows that all building archetypes, regardless of the q-scenario considered, exhibit values of mean annual frequency of collapse that comply with limits available in the literature.

Seismic Evaluation of Steel Moment Resisting Frames (MRFs)—Supported by Loose Granular Soil

Soil underneath a structure might affect the behavior and the overall response of the structure in seismic events. The role of loose soil conditions and the inclusion of soil-structure interaction (SSI) in the analysis are important issues that need to be addressed. Since steel structures are light, two configurations designed as spatial and perimeter are considered to study the effect of soil on the steel structural frames for the same building. The paper provides a parametric analysis on the influence of SSI on the overall performance of MRFs (Moment Resisting Frames) according to the provisions of Saudi Building Code (SBC) [1]. A case study has been developed in which spatial and perimeter moment resisting frames of 12, 6 and 3 stories residential buildings are designed using Saudi Building Code (SBC) prescriptions. A modal response spectrum analysis has been carried out to see the influence of SSI on the fundamental period of vibration, top story displacement and inter-story drift limitations. Moreover, a static non-linear analysis has been performed to investigate the performance of frames, thus allowing to identify the influence of SSI on the structural design of steel MRFs.

More efficient lateral load patterns for seismic design of steel moment-resisting frames

The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural systems and earthquake excitations before they can be used in common practice. The aim of this work was to identify the most suitable lateral load patterns for the seismic design of steel moment-resisting frames. To do this, the non-linear seismic behaviour of three-, five-, seven-, ten- and 15-storey frames designed with nine different lateral load patterns were compared under 20 real and synthetic spectrum-compatible earthquakes using performance parameters such as maximum inter-storey drift, maximum plastic hinge rotation and cumulative damage. It was found that, for the same structural weight, structures designed with more efficient load patterns experienced up to 68% less global damage than their code-based counterparts.

Multi-objective seismic design optimization of steel frames by a chaotic meta-heuristic algorithm

In this study, multi-objective optimization is applied to implement performance-based design of steel moment-resisting frame (SMRF) structures. In order to efficiently achieve this purpose, a chaotic multi-objective firefly algorithm (CMOFA) is proposed to find the Pareto optimal front for the multi-objective performance-based optimum design (MO-PBOD) problem of SMRFs. The structural weight and the maximum inter-story drift at performance levels are taken as the conflicting objective functions of the MO-PBOD problem which should be optimized simultaneously subject to serviceability and ultimate limit-state constraints. In order to illustrate the efficiency of the proposed CMOFA meta-heuristic, two benchmark truss examples and three MO-PBOD examples of SMRFs are presented. The numerical results demonstrate the better computational performance of the proposed CMOFA meta-heuristic in comparison with some existing multi-objective algorithms.

Reliability-based optimum seismic design of structures using simplified performance estimation methods

We present an algorithm for the reliability-based seismic design of structures incorporating approximate performance estimation methods and structural optimization. The proposed algorithm allows the automatic design of steel moment-resisting frames using reliability-based criteria and more specifically design criteria based on the mean annual frequency (MAF) that a limit-state is exceeded. Such criteria allow setting constraints with a clear engineering meaning and help to obtain building designs of improved performance and reduced cost. In this work, we propose a simplified approach that allows to quickly calculate the limit-state mean annual frequencies without significant loss of accuracy. More specifically, we use the static-pushover-to-incremental-dynamic-analysis (SPO2IDA) method, which in essence is a R–μ–T relationship with improved properties. SPO2IDA extracts information from the static pushover curve and produces estimates of the limit-state response statistics that are necessary to implement the reliability-based criteria on the limit-state MAF. The optimization problem at hand is solved with a specifically tailored genetic algorithm. A three and a nine-storey steel moment-resisting frame are used to demonstrate the efficiency of the proposed procedure, leading to efficient building designs within reasonable computing time.

Moment resisting steel frames under repeated earthquakes

In this study, a systematic investigation is carried out on the seismic behaviour of plane moment resisting steel frames (MRF) to repeated strong ground motions. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised due to lack of time. In this work, thirty-six MRF which have been designed for seismic and vertical loads according to European codes are first subjected to five real seismic sequences which are recorded at the same station, in the same direction and in a short period of time, up to three days. Furthermore, the examined frames are also subjected to sixty artificial seismic sequences. This investigation shows that the sequences of ground motions have a significant effect on the response and, hence, on the design of MRF. Additionally, it is concluded that ductility demands, behaviour factor and seismic damage of the repeated ground motions can be satisfactorily estimated using appropriate combinations of the corresponding demands of single ground motions.

A genetic algorithm for design of moment-resisting steel frames

This paper presents computational approaches that can be implemented in a decision support system for the design of moment-resisting steel frames. Trade-off studies are performed using genetic algorithms to evaluate the savings due to the inclusion of the cost of connections in the optimization model. Since the labor costs and material costs vary according to the geographical location and time of construction, the trade-off curves are computed for several values of the ratio between the cost of rigid connection and the cost of steel. A real-life 5-bay 5-story frame is used for illustration. Results indicate that the total cost of the frame is minimal when rigid connections are present only at certain locations. Finally, Modeling to Generate Alternatives--MGA, is proposed to generate good design alternatives as the solution from optimization may not be optimal with respect to the unmodeled objectives and constraints. It provides a set of alternatives that are near-optimal with respect to the modelled objectives and that are also farther from each other in the decision space. Results show that a final design could be chosen from the set of alternatives or obtained by tinkering one of the alternatives.

Optimal seismic design of moment‐resisting steel frames with hysteretic passive devices

AbstractThe effectiveness of hysteretic passive devices to protect and mitigate the response of a structure under seismic loading is well established by both analytical and experimental research. Nevertheless, a systematic and well‐established methodology for the topological distribution and size of these devices in order to achieve a desired structural response performance does not exist. In this paper, a computational framework is proposed for the optimal distribution and design of yielding metallic buckling restrained braces (BRB) and/or friction dampers within steel moment‐resisting frames (MRF) for a given seismic environment. A Genetic Algorithm (GA) is used to solve the resulting discrete optimization problem. Specific examples involving two three‐story, four‐bay steel MRFs and a six‐story, three‐bay steel MRF retrofitted with yielding and/or friction braces are considered. The seismic environment consists of four synthetic ground motions representative of the west coast of the United States with 5% probability of exceedance in 50 years. Non‐linear time‐history analyses are employed to evaluate the potential designs. As a result of the evolutionary process, the optimal placement, strength and size of the dampers are obtained throughout the height of the steel MRF. Furthermore, the developed computational approach for seismic design based upon GAs provides an attractive procedure for design of MRFs with hysteretic passive dampers. Copyright © 2009 John Wiley & Sons, Ltd.

Computational Approaches for Good Alternative Solutions Based Load Resistance Capacity in Design of Steel Moment-Resisting Frames

A modeling technique to generate good design alternatives from optimal design of steel moment resisting frames is proposed. First presented is the development of Genetic Algorithm(GA)-based approaches that enable designers to identify the best locations for rigid connections in a frame. This GA uses a unique cost function that enables the trade-off study between the number of rigid connections and total cost. Second, the optimization formulation is modified to generate alternatives with a cost comparable to that of the optimal solution. It enables engineers to compare different solutions on the basis of the structure’s lateral load resistance capacity along with incidental factors like the location of the rigid connections, number of different section types, column splices etc. An example of a 5-story and 5-bay steel moment resisting frame is provided to illustrate the effectiveness of the proposed study.

Constraint approach to performance-based design of steel moment-resisting frames

An optimization method is proposed for performance-based design of steel moment-resisting frames. The multiple design requirements or targets are incorporated into a multiobjective programming problem, where a new formulation based on the constraint approach is presented for obtaining trade-off solutions. The maximum interstory drift angles against seismic motions of three levels are considered as hard targets that should be strictly constrained in the optimization problem. The maximum floor acceleration and total structural volume are conceived as soft targets that are incorporated as objective functions of the multiobjective programming problem. The proposed constraint approach is applied to two representative steel moment-resisting frames, and the characteristics of their optimal designs considering multiple design targets are investigated.

The response of flush end-plate joints under earthquake loading

An experimental investigation of the seismic behaviour of flush end-plate joints is presented. Eight beam-to-column sub-assemblage specimens are tested under monotonic and cyclic loading conditions. The specimen details were varied to ensure a range of failure modes including both end-plate and bolt yielding. Individual connections displayed the same failure mode in both cyclic and monotonic loading conditions. The experimental results are presented in terms of stiffness, moment capacity, rotation capacity and hysteresis curves. The observed response variables are compared with design values obtained using the mechanical model employed in Eurocode 3. The model is seen to predict the mode of failure well, but to over-predict stiffness and under-predict moment capacity. The implications of the test results for the applicability of this joint type to the earthquake-resistant design of moment-resisting steel frames is discussed.

A unified earthquake-resistant design method for steel frames using arma models

The objective of this paper is to develop a unified earthquake-resistant design method for moment-resisting steel frames, including the design earthquake via a dynamic ARMA model. Important features of this design method are: (i) to make it possible to incorporate inherent uncertain features of design earthquakes into the design process itself through the dynamic ARMA model, (ii) to provide a simplified design formula for a preliminary design of moment-resisting steel frames based upon the concept of stiffness-oriented design and (iii) to facilitate the formulation of a new probabilistic multi-objective optimal design problem aimed at finding the design with the minimum level of designer's dissatisfaction. In this optimal design problem, constraints and objectives are handled in a unified manner after a feasible design is obtained. A design example is presented to demonstrate the validity of this unified design method and to examine the convergence of response statistics. Finally, the generality and practicality of this design method are assessed.