Sway Frames Research Articles

Structure-soil-structure interaction effects on structures retrofitted with tuned mass dampers

This paper investigates the dynamic structure-soil-structure interaction (SSSI) between two adjacent sway frames, replicating closely spaced residential buildings in an urban setting subjected to seismic input motions. The structures are considered with and without external damping mechanisms by means of tuned mass damper (TMD) configurations. Geotechnical centrifuge tests were conducted to address the current lack of experimental case studies into SSSI and uniquely explore the influences from the presence of TMDs and variations in their configurations on SSSI. SSSI was found to significantly alter the response of proximally located urban structures, as was evident from significantly larger rocking amplitudes and changes in frequency response spectra. TMD effects under SSSI were mostly found to amplify an adjacent structure's peak roof acceleration response and inter-storey drift – this was most aggravated when the damper was de-tuned. TMD effects were found to be relatively more pronounced under smaller earthquakes and could certainly cause occupational inconvenience or even damage in adjacent buildings.

Mechanical model for determining the critical load of plane frames with semi-rigid joints subjected to static loads

Abstract The present work deals with the effect of beam-column joint flexibility on the elastic buckling load of plane steel frames. A simple and effective mechanical model is proposed and the corresponding stiffness matrix is presented. The model consists in the development of comprehensive approach taking into account, simultaneously, the effects of the joint rigidity, the elastic buckling load, and this for both sway and non-sway frames. As has been shown by previous research, only one element is required over the length of the element to model stability. This is a marked contribution and advantage of the proposed method, as well as its simplicity, and yet accuracy, to solve practical problem with little computational effort. Also, it includes stability functions in the stiffness matrix, something very often ignored by researchers. Numerical results are obtained for frames with various characteristics and support conditions when three illustrative examples from the literature are presented and discussed. The elastic buckling load is found to be strongly affected by semi-rigid joints and reveals that the proposed model is computationally very efficient with the expressions presented being general. The paper makes reference to the Eurocode 3 approach and those of other researchers in comparing the results. The proposed method is found to be more effective and simple to use, and yielding to very good results.

Axial load effects on flush end-plate moment connections

This numerical study focuses on the behavior of flush, end-plate, moment connections subjected to combined bending moment and axial force. Beams within frames are subjected to lateral loads (e.g. earthquake and wind) in the form of axial forces and bending moments. Thus, both must be considered in seismic design. In pitched-roof portal frames, sway frames or frames with incomplete floors, the level of axial forces in such joints may be significant. To partially fulfill this dual requirement, two distinctive flush, end-plate, moment connections were investigated: one to exhibit thick, connection-plate behavior and the other to exhibit thin, connection-plate behavior. The magnitude of the imposed axial force changes the failure mode. When subjected to reversed cyclic loading, distinctive behaviors between the two end-plate connection types were observed. During cyclic loading, in the axial compressive force phase, there was an increase in the ultimate bending moment, yielding bending moment, initial stiffness, and dissipated energy. Reductions occurred in all of these elements during the tensile axial force phase. As expected, the thin end-plate had notably higher ductility than the thick end-plate connection. In both connections, the maximum moment capacity under compressive axial force nearly equaled 30% of the beam's section yield stress.

Review of the second-order moment amplification factors in AS4100 for the system design approach

The first-order elastic analysis cannot capture the second-order effects owing to the change in structural geometry, such as P-Δ and P-δ effect, which can cause the second-order moment in order to deteriorate the stiffness of a structure. Unfortunately, the first-order elastic analysis is prevalent in the design office and the current practical engineers have not yet well equipped for manipulating the advanced analysis for design purpose. To this end, AS4100 stipulates the design calculation of moment amplification factor for the braced and sway member continuous in a framed structure in Section 4 of the method of structural analysis as a system approach; specifically for an axially compressive loaded column in either a braced or sway frame. However, in this study, it is shown that the moment amplification factors as a system approach is not as effective and sophisticated as the member design approach. In this regard, this paper reviews the moment amplification factor for the second-order effects on a rectangular portal frame with recourse to the first-order elastic analysis, and finally discusses an issue between the second-order moment amplification factor and the member buckling design, which can facilitate the design section of the system approach in AS4100 in alignment with the advanced analy"?>sis for the future system design approach.

Experimental study on blind bolted connections to concrete-filled stainless steel columns

This paper studies the performance of blind bolted connections to concrete-filled stainless steel tubular columns. An experimental investigation was conducted on seven full-scale joints to study the effects of the following parameters: (a) presence of the floor slab or not; (b) with or without binding bars in the connection region; (c) type of steel used for the column (stainless or carbon steel); and (d) loading type (monotonic or cyclic). The experimental results demonstrated the good performance of the blind bolts in this type of connection. No bolt shank fracture was observed in any of the test specimens. The presence of the binding bars slightly enhanced the performance of the blind bolted connections, whereas the presence of composite slabs significantly affected the failure mode, initial stiffness, flexural resistance, and rotation capacity of the joints. Owing to the use of flush end plates, the joint without floor slab can be classified as nominally pinned joint according to EC3. But in the presence of the floor slab, the joint nearly reached its full strength and the stiffness was also significantly increased close to the limit for rigid sway frames. In addition, the test results indicated that the material type of the steel tube had no obvious influence on the joint performance. In contrast, the cyclic loading led to slightly decreased joint strength, but had more obvious detrimental influence on the joint stiffness.

Systems Reliability for 3D Steel Frames Subject to Gravity Loads

The system-based design of steel structures using advanced analysis leads to a more efficient structural design process and achieves a more uniform level of structural system reliability. The main impediment to adopting this method in practical applications is the apparent difficulty in assigning an appropriate resistance factor to structural systems. In this paper, the reliability assessment and derivation of system resistance factors for a series of 3D low-to-mid-rise steel frames are presented, taking into account the inherent uncertainties in material and geometric properties, and the model uncertainty of advanced analysis. Braced and unbraced (sway) frames with regular and irregular configurations are analysed under gravity loads and the system resistance factors are derived for different target reliability levels. The frames are selected to provide different system failure modes such as sway instability and/or member failure. Recommendations are made for the appropriate target reliabilities and associated system resistance factors for use in designing 3D steel frames at system level by advanced analysis.

Effect of initial panel slenderness on efficiency of Strengthening-By-Stiffening using FRP for shear deficient steel beams

The need for strengthening steel structures is as important as it is for concrete structures, or any other aging structure. Strengthening concrete structures by externally bonding thin composite materials in the form of laminates or strips has proven to be an efficient way for enhancing the flexural, shear, and axial strength of deficient elements. Use of external bonding of thin composite material to strengthen steel structures can also be found in literature. This paper presents another effective strengthening technique in which pultruded GFRP sections are bonded to shear deficient regions to enhance the local buckling resistance of thin walled steel structures. Three steel beams with different web thicknesses were tested experimentally with and without GFRP stiffeners to study the efficiency of the new technique; Strengthening-By-Stiffening or SBS. The ultimate shear capacities of the beams were enhanced by a minimum of 30% when one stiffener was used on a beam with a square panel and a maximum of 40% for beams with larger rectangular panel with two stiffeners (one on each side). The initial global stiffness was also enhanced between 5% and 41% for the strengthened beams as a result of the externally bonding the GFRP stiffeners. Unlike the one stiffener configuration which experienced a major load drop at high load levels, the post yielding behavior of the two stiffener configuration exhibited a sustainable load capacity around the peak load without any major load drop. Strain reading from the top and bottom flanges at the loading point revealed that a sway frame mechanism became the main shear resisting mechanism after the critical panel buckled due to shear.

AN ENHANCED IMPERIALIST COMPETITIVE ALGORITHM FOR OPTIMUM DESIGN OF STEEL FRAMES

Development of efficient and robust optimization methods for structural design is one of the most active research fields in structural engineering. Imperialist Competitive Algorithm (ICA) is one of the recent meta-heuristic algorithms proposed to solve optimization problems. In this paper, an Enhanced Imperialist Competitive Algorithm (EICA) is proposed which increases the search space and enables the ICA algorithm to escape from local optima in a fast time. In this algorithm added value is given to a slightly unfeasible solution, based on its distance from the relative imperialist. The performance of the proposed EICA algorithm in optimum design of side sway frames is investigated by comparing the EICA optimum designs of two benchmark side sway frames with the best designs obtained using a number of other meta-heuristic solutions. Results indicate that, in terms of both the design quality and the solution speed, EICA compares favorably with a number of other meta-heuristic optimizers, including the basic ICA.

Improving the Reliability of Measuring Critical Buckling Load in Sway Mode Frames

In the present study a method for improving the reliability of measuring the elastic critical buckling load of sway frames is proposed. The critical load is obtained by extrapolating the dependence between the lateral stiffness and vertical load that acts on the frame up to zero value of the lateral stiffness. The reliability is improved by planning of testing procedure and nearing the testing load to the buckling one. The testing procedure includes planning and correction of the lateral load during the experiments in order to avoid plastic deformations under high vertical loads. Theoretical dependence of lateral stiffness on the vertical load is obtained considering the stiffness in connections between the frame elements is found. Errors due to extrapolation, limited measurements’ quantity and measuring accuracy are considered. The theoretical results are further verified experimentally for various elements connection schemes. It is shown that using linear extrapolation of the dependence between lateral stiffness and vertical load provides high accuracy. Moreover, it’s determined that increasing the maximum testing load decreases the difference between the experimental and analytical values of the buckling load. Therefore the proposed method can be successfully used for testing sway frames in laboratory and real conditions.

Tuned mass damper effects on the response of multi-storied structures observed in geotechnical centrifuge tests

Tuned mass dampers (TMDs) are widely used to reduce vibrations in structures. However, very little research is available on the experimental investigation of TMDs and their performance in soil-structure systems. In this paper, a series of geotechnical centrifuge tests was conducted to investigate the effects of TMDs on the response of a multiple-storey sway frame structure undergoing dynamic soil-structure interaction (SSI). Structural responses were recorded for a wide range of input motion characteristics, damper configurations and soil profiles. The practicality associated with the use of TMDs in the damping of resonant structures in light of unexpected earthquake characteristics different from design earthquakes was experimentally demonstrated. Tuning a TMD to soil-structure system properties rather than fixed-base structural properties was found to double the improvement in damping and reduce the original peak response by nearly half. The potential effectiveness of a de-tuned mass damper in light of significant SSI was also demonstrated.

Story-Based Stability Analysis for Evaluating Story Buckling Load of Frames

This paper presents a kind of optimum modeling method for evaluating system buckling load of plane sway frames, based on the research of the different correction coefficientβ. The buckling load of plane sway frames was calculated by using the optimized method, and the results were compared with those of the ANSYS. It is verified that the simplicity, accuracy and applicability of the method.

Revisiting the moment distribution method: examples of a one-step approach

The moment distribution method (MDM) is revisited in this paper. A one-step analytical approach is presented herein for the moment distribution analysis of indeterminate structures, which is unlike the conventional MDM that requires numerical iteration until convergence. The one-step approach inherits the beauty and simplicity of the conventional MDM, yet it can largely reduce the time and effort spent on numerical iteration. The exact distribution of moments can be easily obtained with merely one cycle of balance and carry over. The presented approach provides a simple and physically intuitive tool for practising engineers to analyse structures at the preliminary design stage or to cross-check numerical results from commercial software. To illustrate the one-step approach, three examples are given herein, namely a continuous beam, a non-sway portal frame and a simple sway frame.

A story buckling method for evaluating system buckling load of plane sway frames

With the intension of developing a simple method for system buckling analysis for engineering practice, a story buckling method for evaluating the system buckling load of a plane rigid frame is suggested. The method is developed based on the idea that at lower modes a plane sway frame buckles in story and story stiffness is getting to zero as the system getting close to the corresponding mode of buckling at that story. The stiffness of any story of a plane sway frame can be found with the stiffness without loading and then modified by a negative stiffness which represents the effect of vertical loads on the horizontal stiffness. P-Δ effect is first considered independently by letting the modified stiffness equal to zero and the system buckling load by first order analysis is obtained. To take P-δ effect into account, the buckling load from the first order analysis is modified with a modification factor and an estimation of buckling load of the whole system is obtained. Application examples are presented and the results are compared with those from FEA of the whole system. The simplicity and accuracy of the suggested method are demonstrated. The restraints of the method for application are discussed.

Analytical assessment of steel frames progressive collapse vulnerability to corner column loss

Most of the approaches to the progressive collapse analysis of steel frames have focused so far on computational methods which try to capture the solution of the system responding to localized damage. For the case of progressive collapse, damage is included in the model through the removal of a key element of the structure. The computational difficulty of these approaches, however, makes it very hard for practicing engineers to perform these analyses. For that reason, it is very important for the engineering community to develop simple and reliable analytical tools which could provide useful information on the response of a structure to a column loss. This paper applies a threat-independent analytical method regarding the corner column loss case, which has been presented by the author in previous papers to a wide range of symmetric and non-symmetric steel moment-resisting (sway) frames. The analytical and simple method can indicate the collapse mechanism of a steel frame for the case of a corner column loss through the development of critical ductility curves. The impact of the number of floors, the column removal location, the vertical irregularity and the design of the frames is also studied.

New simple equations for effective length factors

In most current codes of design steel members and frames, specifications for the design of compression columns or of beam-column use the effective length factor; K. The effective length factor is employed to facilitate the design of framed members by transforming an end-restrained compressive member to an equivalent pinned-ended member. The effective length factor is obtained by solving the exact equations numerically which require many routine calculations or by using a pair of alignment charts for the two cases of braced frames and sway frames. The accuracy of these charts depends on the size of the chart and the reader’s sharpness of vision. Instead of using complicated equations or charts, simple equations are required to determine the effective length factor directly as a function of the rotational resistant at column ends (GA, GB). In this paper, new simple and accurate equations for effective length factors are presented using multiple regressions for tabulated exact values corresponding to different practical values of the rotational resistance at column ends (GA, GB). The investigated equations are more accurate than equations that are recommended in some steel constructions codes. Comparisons between the results of the present equations and those obtained by equations presented in previous researches with those obtained by exact solutions are also given in this paper.

Influence of shear deformation of exterior beam-column joints on the quasi-static behavior of RC framed structures

In the analysis and design of reinforced concrete frames beam-column joints are sometimes assumed as rigid. This simplifying assumption can be unsafe because it is likely to affect the distributions of internal forces and moments, reduce drift and increase the overall load-carrying capacity of the frame. This study is concerned with the relevance of shear deformation of beam-column joints, in particular of exterior ones, on the quasi-static behavior of regular reinforced concrete sway frames. The included parametric studies of a simple sub-frame model reveal that the quasi-static monotonic behavior of unbraced regular reinforced concrete frames is prone to be significantly affected by the deformation of beam-column joints.

Finite Element Method for Solving Bucking Load of Semi-Rigid Steel Frame

Took two layers of single span lateral sway semi-rigid connecting steel frame to bear vertical load function as the research object, adopting finite element method for solving the bucking load of the whole losing the stability of the semi-rigid connecting steel frame. Using based on the energy method and the three parabolic interpolation deflection curve function to obtain the relationship between the both element ends of internal force and displacement and introducing semi-rigid beam element stiffness matrix and geometric stiffness matrix of element integrate the global stiffness matrix which contains the flexibility of the connections and the component geometry nonlinear, thus deducing the stability characteristic equation of semi-rigid steel frame. And the MATLAB language composition program is applied to calculate the buckling load of overall losing stability of the semi-rigid steel frame, thus obtaining the buckling load of semi-rigid steel frame. The method is a very effective numerical calculating method which can solve the stability problems of relatively complicated stress conditions or relatively complicated structure composition conditions and it can also satisfy the requirement of higher calculation accuracy, easy for programming and calculation and of great practicability.

A prediction-error-based method for data transmission and damage detection in wireless sensor networks for structural health monitoring

In this work, a prediction-error-based method that aims to reduce the amount of data transmission and storage in structural health monitoring wireless sensor networks (WSN) while keeping the damage detection capabilities intact is presented. WSNs offer tremendous promise for accurate and continuous structural monitoring using a dense array of inexpensive sensors and possess many advantages over conventional wired systems, particularly for large civil infrastructures. This paper validates the studied approach with the data collected during a test on a three-story steel frame mounted at the ELSA laboratory of the EU Joint Research Center in Ispra, Italy. The frame is tested with and without steel bracing, which results in non-sway behavior and sway frame responses. The excitation is provided by a shaker mounted on top of the frame. Accelerometer signals are collected by a multi-channel data acquisition system. The proposed method has been tested extensively via recorded experimental data and it offers considerable saving in transmitted energy while at the same time keeping the ability to detect changes or damage in the structure.

A new simplified analytical design method for steel and composite sway frames

Eurocode 4 is the European design code for composite construction; in its so-called EN 1994-1-1 version, the design of “non-sway buildings” is mainly covered. As a result, EC4 focuses on the checking of structural elements like beams, columns, slabs and joints. However, in the last years, the construction of taller buildings and larger industrial halls without wind bracing systems tends to make global instability a relevant failure mode, which is not well covered by Eurocode 4. Recently, intensive experimental, numerical and theoretical investigations have been carried out at Liège University. The latter aimed at improving the knowledge in the field of sway composite building frames and at developing appropriate design rules. The rotational behavior of the beam-to-column composite joints is one of the key aspects of the problem to which a special attention has been paid. This paper reflects investigations carried out at Liège University on this topic. In particular, an innovative simplified analytical method to predict the ultimate loading factor and the associated collapse mode of both steel and composite frames subjected to static loadings is presented.

Experimental and numerical validation of a new design for three-dimensional semi-rigid composite joints

Semi-rigid composite joints not only have the advantage of optimizing the use of the material, but also of providing lateral stiffness for sway frames. By means of semi-rigid joints, the lateral stability of the structure may rely on the stiffness and ductility of the joints, thus avoiding bracing systems. These advantages may even increase when the joints are designed as semi-rigid in both axes. In this case, the joint behaves in a three-dimensional way that includes an interaction between the major and the minor axis of the column.In this paper, a new design for three-dimensional semi-rigid composite joint is proposed and tested in order to improve the behaviour and obtain the benefits of semi-rigidity when both the major and minor axis are included. Thus, the proposed design involves beams that are attached in a semi-rigid manner to both, the major and minor axes of the column.The experimental program consists in one 3D semi-rigid composite internal joint under proportional loads, another internal joint subjected to non-proportional loads and one facade joint. These tests provide information as to whether the joints satisfy the requirements of the Eurocodes 3 and 4 (EC3 and EC4) in terms of ductility, stiffness and resistance. Also the possible interactions between the major and minor axes of the proposed joint that are caused by the loads and/or the geometry are studied.Simultaneously, finite element modelling and analysis have been carried out and calibrated against the experimental results. These models have been performed with the aim of finding tools and ways to characterize and analyse the proposed joint design.Design guidelines are also provided for the use of this joint, and some additions and modifications to the Eurocode component method are proposed.