Multi-mode Pushover Procedure for Deformation Demand Estimates of Steel Moment-resisting Frames

Massimiliano Ferraioli 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.2

The main objective of the paper is the development and evaluation of a multi-mode pushover procedure for the approximate analysis of the seismic response of steel moment-resisting frames. A generalized force vector derived from modal combination simulates the instantaneous force distribution acting on the structure when the interstorey drift reaches its maximum value during dynamic response to a seismic excitation. Considering the interstorey drift for each floor, a set of generalized force vectors (each associated to maximum drift at one story) is applied separately to the structure until the corresponding target interstorey drift is attained. The maximum value of each response parameter is obtained from the envelope of results. This multi-run and multi-mode pushover procedure allows a simple implementation, reducing the computational effort compared with adaptive nonlinear static procedures and with nonlinear response history analysis. Furthermore, it does not suffer from the statistical combination of inelastic modal responses calculated separately. Both effectiveness and accuracy are verified through a comparative study involving regular steel moment resisting frames subjected to various acceleration records. The results are finally compared with those obtained from other nonlinear static procedures and with the “exact” values from nonlinear response history analysis. It is demonstrated that the proposed procedure is able to accurately predict the seismic demands of steel moment-resisting frames. In low- and middle-rise frames, the error of interstorey drift ratios of the proposed procedure is in the range 5.8-20.8% when the intensity level of the input ground motion varies in the range 0.2-0.8 g. In high-rise frames the error of interstorey drift ratios is in the range 6.38-20.9%.

Enhancing seismic performance of ductile moment frames with delayed wire-rope bracing using middle steel plate

Akram Ghalandari,Mohammad Reza Ghasemi,Babak Dizangian 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.2

Moment frames have considerable ductility against cyclic lateral loads and displacements; however, sometimes this feature causes the relative displacement to exceed the permissible limits. This issue can bring unfavorable hysteretic behavior on the frame due to the reduction in the stiffness and resistance against lateral loads. Most of common bracing systems usually control lateral displacements through increasing stiffness while result in decreasing the capacity for energy absorption. This has direct effect on hysteresis curves of moment frames. Therefore, a system that is capable of both having the capacity of energy absorption as well as controlling the displacements without a considerable increase in the stiffness is quite important. This paper investigates retrofitting of a single-storey steel moment frame using a delayed wire-rope bracing system equipped with the ductile middle steel plate. The steel plate is considered at the middle intersection of wire ropes, where it causes cables to be continuously in tension. This integrated system has the advantage of reducing considerable stiffness of the frame compared to cross bracing systems as a result of which it could also preserve the frame's energy absorption capacity. In this paper, FEM models of a delayed wire-rope bracing system equipped by steel plates with different geometries have been studied, validated, and compared with other researchers' laboratory test results.

Strengthening of the panel zone in steel moment-resisting frames

Abedini, Masoud,Raman, Sudharshan N.,Mutalib, Azrul A.,Akhlaghi, Ebrahim Techno-Press 2019 Advances in computational design Vol.4 No.4

Rehabilitation and retrofitting of structures designed in accordance to standard design codes is an essential practice in structural engineering and design. For steel structures, one of the challenges is to strengthen the panel zone as well as its analysis in moment-resisting frames. In this research, investigations were undertaken to analyze the influence of the panel zone in the response of structural frames through a computational approach using ETABS software. Moment-resisting frames of six stories were studied in supposition of real panel zone, different values of rigid zone factor, different thickness of double plates, and both double plates and rigid zone factor together. The frames were analyzed, designed and validated in accordance to Iranian steel building code. The results of drift values for six stories building models were plotted. After verifying and comparing the results, the findings showed that the rigidity lead to reduction in drifts of frames and also as a result, lower rigidity will be used for high rise building and higher rigidity will be used for low rise building. In frames with story drifts more than the permitted rate, where the frames are considered as the weaker panel zone area, the story drifts can be limited by strengthening the panel zone with double plates. It should be noted that higher thickness of double plates and higher rigidity of panel zone will result in enhancement of the non-linear deformation rates in beam elements. The resulting deformations of the panel zone due to this modification can have significant influence on the elastic and inelastic behavior of the frames.

국내 저층 철골 모멘트골조의 내진설계

김태완 한국지진공학회 2011 한국지진공학회논문집 Vol.15 No.1

현재 국내 철골 모멘트골조 접합부는 대부분 공장제작으로 품질관리가 잘 이루어져 연성능력이 상당한 수준이다. 문헌에 의하면 국내 접합부는 미국 철강협회에서 철골 중간모멘트골조에 대해 제시한 성능 기준을 충분히 만족하고 있다. 그런데 이전 설계기준인 KBC2005에서는 철골모멘트골조에 연성모멘트골조 하나만을 제공하였으나 현 KBC2009 기준은 보통, 중간, 특수모멘트골조로 다양하게 제공하고 있다. 여기서 국내 접합부 형식을 그대로 사용했을 때 어떤 시스템이 적합한지 조사할 필요성이 있다. 따라서 본 연구에서는 KBC2005의 연성모멘트골조와 KBC2009의 중간모멘트골조의 거동을 비교하여 국내에 적합한 설계 방법을 찾고자 하였다. 연구 결과 기존 연성모멘트골조의 설계 계수를 따르더라도 성능목표를 충분히 만족하는 것으로 나타났다. The connection type of steel moment frames in the country is mostly fabricated in factories so that it is fairly ductile due to good quality control. Based on references, the domestic connection satisfies the performance limit for steel intermediate moment frames specified by the AISC. However, the current KBC2009 building code specifies various systems for steel moment frames such as ordinary, intermediate, and special moment frames while the former KBC2005 only did so for a ductile moment frame. This induces the necessity of investigating which system is appropriate in the country when the domestic connection is applied. Therefore, this study was aimed at finding a proper design method by comparing the ductile moment frame in KBC2005 and the intermediate moment frames in KBC2009. The results showed that seismic design parameters for the ductile moment frames can be reasonable for satisfying the performance objective.

Seismic retrofit of welded steel moment connections with highly composite floor slabs

Kim, Sung-Yong,Lee, Cheol-Ho Elsevier 2017 Journal of constructional steel research Vol.139 No.-

<P><B>Abstract</B></P> <P>In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange was prevalent in welded steel moment frames. The composite action due to the presence of a concrete floor slab was speculated as one of the critical causes of the prevalent bottom flange fracture. Close review of past experimental studies recently conducted by the authors clearly indicated that conventional steel moment connections with highly composite slabs are much more vulnerable to the bottom flange fracture. In this study, three seismic retrofit schemes are presented for welded steel moment connections with highly composite floor slabs typical of existing steel moment frames in Korea. Because top flange modification of existing beams is not feasible due to the presence of a concrete floor slab, beam bottom flange or web modifications by using welded triangular or straight haunch and heavy shear tab were cyclically tested. Test results of this study showed that all the retrofit schemes used are effective in eliminating the detrimental effect caused by high composite action and can ensure excellent connection plastic rotation exceeding 4% rad. Side effects resulting from retrofit as well as design recommendations are also discussed.</P> <P><B>Highlights</B></P> <P>This experimental study investigates seismic retrofit schemes for PN-type welded steel moment connections with highly composite floor slabs by using the beam bottom flange or beam web modification. The highlights of this study are:<UL> <LI> Reconfirmed the detrimental effects of high composite action for PN-type connections </LI> <LI> Experimentally verified excellent seismic capacity of all the retrofit schemes studied </LI> <LI> Experimentally verified excellent seismic capacity of all retrofit schemes studied </LI> <LI> Analyzed the unique behaviors of the retrofitted connections </LI> <LI> Discussed the side effects that should be considered in retrofit design </LI> </UL> </P>

Seismic retrofitting of steel moment-resisting frames (SMRFs) using steel pipe dampers

Ali Mohammad Rousta 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.87 No.1

The use of steel pipe dampers (SPD) as fuses or interchangeable elements in the steel moment-resisting frames (MRF) is one of the newest methods for improving seismic performance. In the present study, the performance of steel pipe dampers in MRF has been investigated. Evaluation of MRF with and without SPD models were performed using the finite element method by ABAQUS. For validation, an MRF and MRF with steel pipe dampers were modeled that had been experimentally tested and reported in previous experimental research and a good agreement was observed. The behavior of these dampers in frames of 3, 6, and 9 stories was studied by modeling the damper directly. Nonlinear time history dynamic analysis was used. It was observed that by increasing the number of stories in the buildings, steel pipe dampers should be used to perform properly against earthquakes. The installation of steel pipe dampers in steel moment-resisting frames shows that the drift ratio between the floors is reduced and the seismic performance of these frames is improved.

Behaviour of Steel Deep Beams in Moment Frames with Web Opening Subjected to Lateral Loading

Masoud Hoseinzadeh Asl,Maryam Jahanian 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.5

Due to the sharp change of the lateral load moment diagram in deep beams, the commonly proposed rigid connections may be incapable of proper transferring the plastic region away from the connection face into the beam. That is why prequalifi ed connections of steel moment frames, proposed by diff erent design codes, impose geometrical limitations on the beam spanto- depth ratio, which limits the application of the prequalifi ed connections for short deep beams. The aim of this paper is to suggest details on leading the plastic area away from the column face by making a rectangular web opening at the mid-span of the deep beam. In order to stabilize the weakened area, stiff eners are used around the opening. 52 fi nite element models of deep beams with diff erent geometries of the web openings are investigated. The results show that the use of deep beams with web opening located at mid-span in a steel moment frame is an effi cient method to relocate the plastic hinge away from the connections, resulting in increased ductility. A parametric study is carried out on the eff ect of stiff eners dimensions, web thickness, and corner radius of web opening on behavior of deep beams in moment frames. A step-by-step design algorithm is also propounded for detailing of the web opening and the stiff ener size.

Numerical investigation on seismic behaviors of midrise special moment resistant frame retrofitted by timber-base bracings

Ainullah-Mirzazadah,Saeed-Reza Sabbagh-Yazdi 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.1

Timber is one of the few natural, renewable building materials and glulam is a type of engineering wood product. In the present work, timber-based braces are applied for retrofitting midrise Special Moment Resisting Frame (SMRF) using two types of timber base braces (Timber base glulam, and hybrid Timber-Steel-BRB) as alternatives for retrofitting by traditional steel bracings. The improving effects of adding the bracings to the SMRF on seismic characteristics of the frame are evaluated using load-bearing capacity, energy dissipation, and story drifts of the frame. For evaluating the retrofitting effects on the seismic performance of SMRF, a five-story SMRF is considered unretofitted and retrofitted with steel-hollow structural section (HSS) brace, Glued Laminated Timber (Glulam) brace, and hybrid Timber-Steel BRB. Using OpenSees structural analyzer, the performance are investigated under pushover, cyclic, and incremental loading. Results showed that steel-HSS, timber base Glulam, and hybrid timber-steel BRB braces have more significant roles in energy dissipation, increasing stiffness, changing capacity curves, reducing inter-story drifts, and reducing the weight of the frames, compared by steel bracing. Results showed that Hybrid BRB counteract the negative post-yield stiffness, so their use is more beneficial on buildings where P-Delta effects are more critical. It is found that the repair costs of the buildings with hybrid BRB will be less due to lower residual drifts. As a result, timber steel-BRB has the best energy dissipation and seismic performance due to symmetrical and stable hysteresis curves of buckling restrained braces that can experience the same capacities in tension and compression.

Seismic behavior of steel frames with replaceable reinforced concrete wall panels

Hanheng Wu,Tianhua Zhou,Fangfang Liao,Jing Lv 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.5

The paper presents an innovative steel moment frame with the replaceable reinforced concrete wall panel (SRW) structural system, in which the replaceable concrete wall can play a role to increase the overall lateral stiffness of the frame system. Two full scale specimens composed of the steel frames and the replaceable reinforced concrete wall panels were tested under the cyclic horizontal load. The failure mode, load-displacement response, deformability, and the energy dissipation capacity of SRW specimens were investigated. Test results show that the two-stage failure mode is characterized by the sequential failure process of the replaceable RC wall panel and the steel moment frame. It can be found that the replaceable RC wall panels damage at the lateral drift ratio greater than 0.5%. After the replacement of a new RC wall panel, the new specimen maintained the similar capacity of resisting lateral load as the previous one. The decrease of the bearing capacity was presented between the two stages because of the connection failure on the top of the replaceable RC wall panel. With the increase of the lateral drift, the percentage of the lateral force and the overturning moment resisted by the wall panel decreased for the reason of the reduction of its lateral stiffness. After the failure of the wall panel, the steel moment frame shared almost all the lateral force and the overturning moment.

The beneficial effects of beam web opening in seismic behavior of steel moment frames

Saeed Erfani,Ata Babazadeh Naseri,Vahid Akrami 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.13 No.1

Implementation of openings in beams web has been introduced as an innovative method for improving seismic performance of steel moment frames. In this paper, several steel moment frames have been studied in order to evaluate the effect of openings in beams web. The beam sections with web opening have been modeled as a simplified super-element to be used in designing frames and to determine opening configurations. Finite element models of designed frames were generated and nonlinear static pushover analysis was conducted. The efficient location for openings along the beam length was discovered and the effects of beams with web openings on local and global behavioral characteristics of frames were discussed. Base on the results, seismic performance of steel moment frames was improved by creating openings in beams web, in terms of reduction in stress level of frame sensitive areas such as beam to column connections and panel zones.