Florea Dinu

Performance criteria for MR steel frames in seismic zones

Abstract A parametrical inestigation on different types of steel moment resisting frames (MRF) with rigid and semirigid joints subject to seismic motions is presented in order to establish their performance criteria. Performance criteria of MR steel frames are evaluated through the global and local characteristics, i.e. behaviour factor and damage index. The behaviour factor is related essentially to the maximum inelastic base shear force of the structure obtained from inelastic dynamic analyses, but also related to other methods from the literature. Damage is attributed to plastic rotations at members and joints. A linear damage accumulation low and the rainflow method for counting of cycles are applied. The parametric study is performed via a non-linear dynamic time-history analysis.

Improving the structural robustness of multi-story steel-frame buildings

Although there are numerous hazards that could trigger the progressive collapse of a building, there are limited provisions in related codes regarding the design of structures to withstand exposure to such threats. It is thus expedient to limit the extent of damage to prevent the initiation of progressive collapse. This could be done by usage of the alternate path method, whereby the structure is made to withstand the loss of one or more critical load-bearing elements and prevent disproportionate collapse. In our study, we investigated the resistance of seismically designed steel-frame buildings to progressive collapse, focusing on the contributions of the floor system and beam-to-column connections. The applied element method was used to predict the structural response by nonlinear static and dynamic analyses, with the purpose of determining some robustness criteria, using as reference the ratio of the failure load to the nominal gravity load.

Fatigue Analysis of Moment Resisting Steel Frames

A procedure for the fatigue assessment of steel building structures subjected to earthquakes is presented. The procedure constitutes an extension of the present, high-cycle, fatigue assessment to cases of low-cycle fatigue. It may serve as a basis for the introduction of a fatigue limit state in the earthquake design of steel structures. It may be also used for the damage assessment of existing steel buildings subjected to past earthquakes. By means of parametric studies, the effects of various parameters on the fatigue susceptibility of several moment resisting steel frames are studied. The influence of a number of parameters such as the type of ground motion, type of structural typology, local fatigue behaviour, overall frame design and semi-rigidity of joints on the susceptibility to damage are investigated.

Robustness Based Structural Design: An Integrated Approach for Multi-Hazard Risk Mitigation

Multi-story building structures can suffer local damage or even structural collapse in case of extreme natural or man-made hazards. While all buildings are at a certain risk, some attributes can reduce the risk by reducing the vulnerability. One such attribute is the use of structural systems which can ensure that, in case of abnormal loads or failure of some elements, the collapse is prevented and the risk to occupants is reduced. Mitigation of some specific hazard can also help to reduce the risk, eg. protective barriers against impact or stand-off distance against direct effects of blast. Past experience has shown that structures that are designed according to seismic design philosophy can survive to a multiplicity of hazards. The objective of the paper is the adaptation of seismic design methodology to robust design demands of multistory frame buildings prone to multi-hazard scenarios. The hazard is modeled by removal of critical members. Nonlinear dynamic analyses are carried out in order to evaluate their robustness.

Factors affecting the response of steel columns to close-in detonations

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED2016-0962, within PNCDI III: “Experimental validation of the response of a full-scale frame building subjected to blast load” - FRAMEBLAST (2017-2018).

Multi-Hazard Risk Mitigation through Application of Seismic Design Rules

Multi-story buildings often use steel moment frames as lateral force resisting systems, because such systems would allow architectural flexibility, while providing the strength, stiffness, and ductility required to resist the gravity, wind, and seismic loads. Steel moment frames on which capacity design concepts are applied to resist earthquake induced forces, are generally considered robust structures, with adequate resistance against collapse for other extreme hazards, for example blast or impact. Starting from this point, the present paper summarizes the results of some recent studies carried out in the Department of Steel Structures and Structural Mechanics and CEMSIG Research Center from Politehnica University Timisoara, aiming to evaluate the influence of beam-to-column joints, designed to satisfy seismic design requirements, on the progressive collapse resistance of multi-story steel frame buildings.

DUAL STEEL FRAMES WITH RE-CENTERING CAPACITY AND REPLACEABLE STEEL SHEAR PANELS

Abstract. Structures that have replaceable thin-walled steel shear panels are efficient structural systems for resisting seismic loads owing to their high initial stiffness and reliable energy dissipation capacity. In order to reduce the economic losses (loss of building operation, cost of repairing), the dissipative system may be designed to be easily removed and replaced if damaged by an earthquake. When the shear panels and moment resisting frames are used together (dual system), allowing the moment resisting frame to remain in elastic reduces the residual displacement after an earthquake and provides the re-centering capacity that is required for removing and replacing the damaged walls.

Global Ductility of Dual Steel Frames with Replaceable Dissipative Shear Walls

Abstract The paper presents the results of a numerical program that was used to investigate the seismic performance of dual steel frames with dissipative shear walls. Nonlinear static and dynamic analyses were employed in order to evaluate the global ductility and the q factor for a twelve story building. The influence of the q factor on the estimated level of damage and post-earthquake intervention strategy was investigated. The dynamic analyses were conducted using two groups of accelerograms, selected to match the response spectra of two types of grounds. The numerical models were validated against experimental tests. The results show that q factor values adopted in design influence the level of damage. If re-centering capacity is properly controlled by design, the replacement of damaged walls can minimize the time and cost of intervention, thus supporting disaster resilience of buildings