Strength Degradation Modelling of Structures Subjected to Earthquakes and Fire (original) (raw)

Significance of Modeling Deterioration in Structural Components for Predicting the Collapse Potential of Structures Under Earthquake Excitations

Geotechnical, Geological and Earthquake Engineering, 2010

A primary objective of good earthquake engineering is to provide an adequate margin of safety against collapse. Collapse prevention is not an absolute goal, because ground motion uncertainties and economic constraints will always necessitate the acceptance of a small probability of collapse. Assessment of this small probability of collapse requires the ability to predict, with sufficient confidence, the response of structures all the way to collapse. This aspect of performance-based earthquake engineering has posed major challenges, some of which are discussed in this paper.

Seismic performance of strength degraded structures

2008

Traditionally, performance assessment of a structure is based on trading off strength demand with ductility demand. In high seismicity region, the design provisions are based on the concept of conservation of energy; such guidelines (FEMA 273) recommend a very low drift capacity for strength degraded structures. Furthermore, the application of these guidelines, results in most of the strength degraded structures deemed unsafe when subjected to earthquake excitations in low and moderate seismic regions. This paper presents results of nonlinear time history analyses (THA) for such strength degraded structures for a range of near-field and far-field earthquake scenarios of different M-R combinations. Fragility curves defining probability of failure of structures have been developed. The insensitivity of the probability of failure of the URM wall on its height (i.e. vertical span length) is an interesting finding in this study. Also, the extent of strength degradation in an unreinforced...

Nonlinear Performance and Damage Potential of Degraded Structures under Long Duration Earthquake

2016

Occurrences of mega earthquakes have been reported more frequently in recent years. Due to their long duration and large number of cycles, the degradation of both stiffness and strength have significant effects on structural performance and damage accumulation. On May 12, 2008, a large Ms 8.0 earthquake occurred in the Longmenshan Fault zone in Wenchuan County, Sichuan Province, China. This earthquake lasted for over 350 seconds and caused more than 69,000 casualties and about 124 billion USD in financial losses. Just five years later, on April 20, 2013, a large Ms 7.0 earthquake occurred at the same Longmenshan Fault zone in Lushan County (about 90km from the Wenchuan epicenter) with a typical duration of 80 seconds. Both earthquakes hit rural countries in western China where low-rise buildings and self-built masonry in-filled reinforced concrete structures are prevalent. Significant damage and collapse were reported in many reconnaissance reports. For both earthquakes, a significa...

Interaction of Local and Global Structural Behavior of Buildings under Catastrophic Loadings

Response of Structures to …, 2003

Designing structures safe and reliable is the most important issue in structural engineering. Especially the effects of catastrophic loadings like terrorist attacks on structures-the events of September 11, 2001 in New York City is only one disastrous but the most impressive example-lead to an increasing demand in designing buildings for natural and/or technical hazard loadings like explosion, blast and impact. Such high dynamic loadings have the capability to release large amounts of energy within microseconds, and to cause high pressures in the kilobar range and high strain rates in the affected bodies. Thus, design tasks are challenging for engineers in practice as well as for researchers. Unfortunately, structural dynamics methods are often insufficient to treat these highly dynamic processes. Hence, this paper presents a concept how to deal with hazard loadings in the designing calculation of the local and global structural response. In detail, terrorist threats have been classified with respect to the loading effects on the structure. As an example, the local failure mechanisms are evaluated first, considering detonation loadings on a concrete based structural element. From this, the individual residual carrying capacity is determined, which is included for all damaged structural elements in the full computer model of the structure. The global response including the residual carrying capacity of the structure is calculated. From gained knowledge of structural response, new standards can be developed to design and/or to retrofit buildings. OVERVIEW AND CLASSIFICATION Loading: static-dynamic-high dynamic Buildings are designed to resist loadings, which affect a structure during its lifetime. Usually, these loads are dead load, service load, snow, wind, thermal forces, etc. These loads are commonly assumed to be equivalent static loads. Civil engineers are usually well educated to handle such loads. In the past two years, the demand of building owners, to design their buildings also for loadings from terrorist attacks, has increased. Most engineers do not have the knowledge, experience and proper technology to calculate terrorist effects accurately. For the classification of the effects of high dynamic loadings on structures their specific parameters are given and compared with each other (Table 1). The data, based on different publications, is collected and supplemented. It does not claim to be complete, but gives reference values for the most strained structural parts (e.g. in Bischoff & Perry [1], Zukas et al. [2], Gebbeken & Ruppert [3]).

The Effect of Structural Degradation on the Seismic Behavior of Structures

The aim of this paper is to illustrate the change in dynamic behavior of structures associated with system degradation. The acceptance of plastic hinges occurrence in a building according to the seismic design standards is not a safe method for slow earthquakes, as Vrancea intermediate earthquakes, when can result important building damages or even collapse. The paper presents new solutions to increase reliability and safety of a new or an existing building at seismic actions. It consists in controlling, limiting and damping the seismic movements using the mechanical devices SERB.

MODIFICATION OF THE BUILDING DYNAMIC RESPONSE DUE TO STRUCTURAL DAMAGING DURING STRONG EARTHQUAKEs

The paper is an analysis of buildings behavior during strong earthquakes, considering the modifications of the structural dynamic characteristics due to strong earthquake -generated damages. The study is focused on the difference in a building behavior, function of the mode the structure is situated relative to the seismic ground motion from the spectral point of view: above resonance or below resonance. Experimental and simulation results are presented for simplified mechanical models of building structures with stiffness degradation. As a convenient measure of the effect of duration and severity of the building seismic loads, the total energy dissipated through hysteresis is considered.

Analysis of the Progressive Collapse of Buildings under High Temperatures Using Successive Approximation Technique

Journal of Civil Engineering and Architecture

This paper presents an investigation of the disproportionate collapse of multi-store steel buildings in a natural fire situation due to the progressive failure of their columns. For this purpose, it is intended to evaluate the effects of the redistribution of stress and vertical displacements of columns with the evolution of the temperature addressing, also, the impacts of the localized faults of these structural elements. In addition, another objective of this paper is the development of a practical analysis approach, which is called by successive approximations. As a methodology, advanced computational techniques were developed to predict the structural behavior of the building as the temperature reduces the strength and stiffness of its structural elements. For the parametric study, the overall response of the building was investigated through fire simulations in many columns. The results showed that the phenomenon of redistribution of stresses that occur during the heating period is essentially due to the reduction in the modulus of elasticity of the steel. In addition, the study pointed out that the use of advanced computational techniques through the use of successive approximations technique is an excellent alternative to study the progressive collapse of buildings subject to high temperatures.

Nonlinear Analysis of a Steel Frame Structure Exposed to Post-Earthquake Fire

Fire, 2021

The probability of extreme events such as an earthquake, fire or blast occurring during the lifetime of a structure is relatively low but these events can cause serious damage to the structure as well as to human life. Due to the significant consequences for occupant and structural safety, an accurate analysis of the response of structures exposed to these events is required for their design. Some extreme events may occur as a consequence of another hazard, for example, a fire may occur due to the failure of the electrical system of a structure following an earthquake. In such circumstances, the structure is subjected to a multi-hazard loading scenario. A post-earthquake fire (PEF) is one of the major multi-hazard events that is reasonably likely to occur but has been the subject of relatively little research in the available literature. In most international design codes, structures exposed to multi-hazards scenarios such as earthquakes, which are then followed by fires are only an...

Damage-dependent vulnerability curves for existing buildings

Earthquake Engineering & Structural Dynamics, 2013

Seismic behavior of damaged buildings may be expressed as a function of their REsidual Capacity (REC), which is a measure of seismic capacity, reduced by damage. REC can be interpreted as the median value of collapse vulnerability curves. Its variation owing to damage is a useful indication of increased building vulnerability. REC reduction, indicating the lowering of seismic safety after an earthquake (performance loss, PL), represents an effective index for assessing the need of seismic repair/strengthening after earthquakes. The study investigates the applicability of a pushover-based method in the analysis of damaged structures for the case of existing under-designed RC buildings. The paper presents a systematization of the procedure in an assessment framework that applies the capacity spectrum method based on inelastic demand spectra; furthermore, the vulnerability variation of a real building is investigated with a detailed case study. The behavior of damaged buildings is simulated with pushover analysis through suitable modification of plastic hinges (in terms of stiffness, strength and residual drift) for damaged elements. The modification of plastic hinges has been calibrated in tests on nonconforming columns. The case study analysis evidenced that, for minor or moderate damages, the original structural displacement capacity was only slightly influenced, but the ductility capacity was significantly reduced (up to 40%) because of the increased structure deformability. This implied performance loss in the range 10%-20%. For severe damages the PL ranged between 41% and 56%. Local mechanism types exhibit PL nearly double with respect to global mechanism types. realistic estimate of evolving seismic risk during a seismic sequence, suitable modeling of building vulnerability variation should be considered. The variation in building safety owing to seismic damage is implicitly recognized by building tagging procedures, which are applied after major seismic events . In such procedures, post-earthquake safety is generally evaluated by visual inspection, with an expert assessment of damage level, extent and the related building usability by a team of experienced practitioners. However, if varied vulnerability is to be considered within a consistent quantitative assessment framework, analytical modeling of building performance loss (PL) is preferable.

Numerical modeling of building structures in fire conditions

Proceedings of the workshop …, 2010

Numerical modelling is a very useful tool to predict the fire resistance of a structure, or to reproduce artificially what has happened during a real fire. SAFIR, a non linear computer code developed at the university of Liege-Belgium, is specifically written for modeling the behavior of structures subjected to fire. It allows a determination of the temperatures in the structure resulting from the fire and, in a subsequent analysis, determination of the successive positions of equilibrium of the structure until collapse. SAFIR program accommodates various elements for different idealizations, different calculation procedures and several material models incorporating stress-strain behaviour. The elements include 2-D SOLID, 3-D SOLID, BEAM, SHELL and TRUSS elements. The stress-strain material laws are generally linear-elliptic for steel and nonlinear for concrete. This paper introduces the main hypotheses, the possibilities and the validity of this program. Comparisons of test results and simulated results by SAFIR program for concrete structures, steel structures and concrete-steel composite structures are presented.