Seismic behavior of concentrically braced frames designed using direct displacement-based method

Dipti Ranjan Sahoo,Ankit Prakash 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.1

This study is focussed on the evaluation of seismic performance of concentrically steel braced frames (CBFs) designed using direct displacement-based (DDBD) method. Design displacement profi le in this method is derived from the inelastic mode shape normalized based on fi rst story displacement. Design base shear of a structure is determined using design displacement spectrum and the equivalent viscous damping. Two low- and medium-rise CBFs, namely, 3-story and 6-story, are designed using DDBD method as well as current practice. These study frames are modelled and analysed in a computer software OpenSEES to compare their seismic performance under a set of selected ground motions. Braces are modelled using force-based fi bre-discretized non-linear beam-column elements simulating the eff ects of inelastic buckling, large strain and low-cycle fatigue. The main parameters investigated are the maximum story displacements, the interstory drifts, the residual drifts and the yield mechanisms. DDBD frames exhibited the improved seismic response as compared to those design as per current practice.

Behavior of Unstiffened Steel Plate Shear Wall with Simple Beam-to-column Connections and Flexible Boundary Elements

Dipti Ranjan Sahoo,Balsher Singh Sidhu,Arunesh Kumar 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.1

This study investigates the effect of type of beam-to-column connections on the overall performance of steel plate shear wall(SPSW) systems under lateral loading condition. An analytical study using finite-element analysis has been conducted on a twostorySPSW system with rigid and pinned beam-to-column connections having constant panel aspect ratio and plate slendernessratio. All boundary elements are designed as per the current code provisions. The influence of the type of connections betweenthe web plates and the boundary elements on the overall performance of SPSW systems is also studied. In addition, the behaviorof SPSW system with flexible boundary members along with pinned beam-to-column connections is also investigated underlateral loading condition. An experimental study has been carried out on a two-story SPSW specimen with flexible boundaryelements to investigate its overall performance under the slow-cyclic loading. Based on the analytical and experimental results,various design issues of SPSW systems are discussed.

Effect of Chord Configuration and Spacing on Cyclic Flexural Response of Built-up Columns

Sajal Sarkar,Dipti Ranjan Sahoo 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.2

As per the current codes of practice, the design of battens of a built-up steel column depends on the level of axial load. These columns may not reach their plastic moment capacities under the lateral loading due to the premature instability of main chords in the expected plastic hinge regions. In this study, the cyclic performance of built-up battened columns is analytically evaluated under the gradually-increasing lateral displacements and the constant axial loads using a finite element software ABAQUS. The main parameters varied are the chord spacing, the column slenderness ratio, the level of axial load, and the chord configuration. Ninety-eight FE models of battened columns are analysed in this study in which the hot-rolled steel channel or I-Sections are used as the main chords. The analytical results showed that the built-up columns made up from I-sections have better lateral strength and ductility as compared to the Channel sections for nearly same values of axial load and slenderness ratio. Based on the analytical results, the limiting values of chord spacing, slenderness ratio and level of axial loads are proposed in order to delay the effect of instability on their lateral load resistance. Further, the interaction between axial load-moment capacity of built-up columns is discussed for various types of chord configurations.

Study on Detailing of Structural Steel Section on Lateral Behavior of SRC-RC Transfer Columns

Abhishek Jain,Dipti Ranjan Sahoo 한국강구조학회 2024 International Journal of Steel Structures Vol.24 No.2

Transfer columns are the essential elements in a building frame structure wherein some stories are constructed with steelreinforced concrete (RC) columns and others with RC columns. The stories with transfer columns may suff er severe damage due to sudden changes in strength and stiff ness along their heights. This study investigates the structural behavior of transfer columns subjected to axial compressive loading and bending about major/minor axes. Forty transfer columns are modeled in the fi nite element software ABAQUS to study their failure mechanism, lateral bearing capacity, and ductility ratios. The parameters investigated are the levels of embedment length of the structural steel, and the detailing of lateral ties and the base plate at the truncation zone in the column. It is concluded that hybrid columns have higher lateral strengths than the RC columns but exhibit limited ductility due to the sudden shear failure. The specimen with structural steel extended by 50–60% of clear column height exhibited improved ductility. The precipitous failure of the transfer column is alleviated with the provision of a base plate and anchor bolts at the end of the structural steel section.

Analytical Investigation on Cyclic Response of Buckling-restrained Braces with Short Yielding Core Segments

Muhamed Safeer Pandikkadavath,Dipti Ranjan Sahoo 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

Buckling-restrained braced frames (BRBFs) are considered to be one of the efficient lateral force-resisting systems used in buildings located in the seismically active regions. Nearly symmetric hysteretic response of buckling-restrained braces (BRBs) in tension and compression due to the yielding of steel core plates helps the BRBFs to withstand the seismic excitations without causing any extensive damage to the primary frame members. However, BRBFs may exhibit the excessive post-earthquake residual drift response due to the low axial stiffness of BRBs under the strong ground motions. A reduction in the yielding core segments of BRBs results in the improved elastic and post-elastic axial stiffness of BRBs which may help in controlling the excessive residual drift response. This study is focussed on the analytical evaluation of hysteretic response of BRBs of varying lengths using finite element (FE) software. The results of FE study are further used to evaluate the inter-story and residual drift response of a 3-story braced frame fitted with BRBs of short core lengths (referred as SBRBF). Nonlinear dynamic analysis results of SBRBF are compared with the conventional BRBF and concentrically braced frame (CBF). It is concluded that the optimum reduction in yielding core lengths of BRBs can improve the overall seismic response of BRBFs with a reduction in the residual drift response.

Effect of Loading History and Restraining Parameters on Cyclic Response of Steel BRBs

Ahmad Fayeq Ghowsi,Dipti Ranjan Sahoo 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.4

This study presents a numerical modelling and prediction of cyclic response of all-steel buckling-restrained braces (BRBs) under diff erent loading histories using a fi nite element software ABAQUS. The numerical models are validated by comparing the predicted hysteretic response, core fracture, energy dissipation and displacement ductility with the results of a past experimental study. Later, the validated numerical model is used in a parametric study to investigate the infl uence of coeffi cient of friction and clearance between the steel core and restrainers, the length of yielding core segment and the position of stoppers on core segments on the cyclic response of steel BRBs. The coeffi cient of friction is varied in the range of 0–0.5, whereas the gap value is varied in the range of 0–5 mm. The main parameters studied are the hysteretic response, axial resistance, instance of core fracture and energy dissipation response. Based on the analysis results, the optimum values of friction coeffi cient, gap, length of yielding core and stopper orientation have been recommended for steel BRBs.

Mitigation of seismic drift response of braced frames using short yielding-core BRBs

Muhamed Safeer Pandikkadavath,Dipti Ranjan Sahoo 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.3

Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.

Seismic Performance of Buckling-restrained Braced Frames with Varying Beam-column Connections

Ahmad Fayeq Ghowsi,Dipti Ranjan Sahoo 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.4

The effect of beam-column connections and brace configurations on the overall seismic response of a medium-rise bucklingrestrainedbraced frame (BRBF) is analytically evaluated in the present study. Two types of brace configurations (chevron andDouble-X) and a combination of the moment-resisting and the non-moment-resisting beam-column connections are considered. A total of five design cases are studied for a seven-story BRBF in which a constant value of response reduction (R) factor equalto 8 is considered in the design. Nonlinear dynamic analyses are carried out for all study frames for an ensemble of forty groundmotions representing the DBE and MCE hazard levels. Fragility curves are developed for all study frames considering theinterstory drift ratio and residual drift ratio as the damage parameters. Results showed that a higher value of response reductionfactor should be adopted in the design of BRBFs for both pinned and rigid beam-column connections. Further, in order toachieve the desired seismic performance of BRBFs, Double-X brace configurations and rigid beam-column connections at thealternate story levels should be used.

Evaluation of seismic strengthening techniques for non-ductile soft-story RC frame

Karki, Prajwol,Oinam, Romanbabu M.,Sahoo, Dipti Ranjan Techno-Press 2020 Advances in concrete construction Vol.9 No.4

Open ground story (OGS) reinforced concrete (RC) buildings are vulnerable to the complete collapse or severe damages under seismic actions. This study investigates the effectiveness of four different strengthening techniques representing the local and global modifications to improve the seismic performance of a non-ductile RC OGS frame. Steel caging and concrete jacketing methods of column strengthening are considered as the local modification techniques, whereas steel bracing and RC shear wall systems are selected as the global strengthening techniques in this study. Performance-based plastic design (PBPD) approach relying on energy-balance concept has been adopted to determine the required design force demand on the strengthening elements. Nonlinear static and dynamic analyses are carried out on the numerical models of study frames to assess the effectiveness of selected strengthening techniques in improving the seismic performance of OGS frame.. Strengthening techniques based on steel braces and RC shear wall significantly reduced the peak interstory drift response of the OGS frame. However, the peak floor acceleration of these strengthened frames is amplified by more than 2.5 times as compared to that of unstrengthened frame. Steel caging technique of column strengthening resulted in a reasonable reduction in the peak interstory drift response without substantial amplification in peak floor acceleration of the OSG frame.

Discussion of “Seismic Performance of Buckling-restrained Braced Frames with Varing Beam-column Connections”

Jong Wan Hu,Ahmad Fayeq Ghowsi,Dipti Ranjan Sahoo 한국강구조학회 2014 International Journal of Steel Structures Vol.14 No.3