Investigating the Effect of Prior Damage on the Post-earthquake Fire Resistance of Reinforced Concrete Portal Frames

Hamid Reza Ronagh,Behrouz Behnam 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.4

Post-earthquake fire (PEF) can lead to a rapid collapse of buildings that have been partially damaged as a result of a prior earthquake. Almost all standards and codes for the design of structures against earthquake ignore the risk of PEF, and thus buildings designed using those codes could be too weak when subjected to a fire after an earthquake. An investigation based on sequential analysis inspired by FEMA356 is performed here on the immediate occupancy (IO), life safety (LS) and collapse prevention (CP) performance levels of two portal frames, after they are pushed to arrive at a certain level of displacement corresponding to the mentioned performance level. This investigation is followed by a fire analysis of the damaged frames, examining the time taken for the damaged frames to collapse. As a point of reference, a fire analysis is also performed for undamaged frames and before the occurrence of earthquake. The results indicate that while there is minor difference between the fire resistances of the fire-alone situation and the frames pushed to the IO level of performance, a notable difference is observed between the fire-alone analysis and the frames pushed to arrive at LS and CP levels of performance and exposed to PEF. The results also show that exposing only the beams to fire results in a higher decline of the fire resistance, compared to exposing only the columns to fire. Furthermore, the results show that the frames pushed to arrive at LS and CP levels of performance collapse in a global collapse mode laterally, whereas at the IO level of performance and fire-alone situation, the collapse mechanism is mostly local through the collapse of beams. Whilst the investigation is conducted for a certain class of portal frames, the results confirm the need for the incorporation of PEF into the process of analysis and design, and provide some quantitative measures on the level of associated effects.

Investigating the Effect of Prior Damage on the Post-earthquake Fire Resistance of Reinforced Concrete Portal Frames

Ronagh, Hamid Reza,Behnam, Behrouz Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.4

Post-earthquake fire (PEF) can lead to a rapid collapse of buildings that have been partially damaged as a result of a prior earthquake. Almost all standards and codes for the design of structures against earthquake ignore the risk of PEF, and thus buildings designed using those codes could be too weak when subjected to a fire after an earthquake. An investigation based on sequential analysis inspired by FEMA356 is performed here on the immediate occupancy (IO), life safety (LS) and collapse prevention (CP) performance levels of two portal frames, after they are pushed to arrive at a certain level of displacement corresponding to the mentioned performance level. This investigation is followed by a fire analysis of the damaged frames, examining the time taken for the damaged frames to collapse. As a point of reference, a fire analysis is also performed for undamaged frames and before the occurrence of earthquake. The results indicate that while there is minor difference between the fire resistances of the fire-alone situation and the frames pushed to the IO level of performance, a notable difference is observed between the fire-alone analysis and the frames pushed to arrive at LS and CP levels of performance and exposed to PEF. The results also show that exposing only the beams to fire results in a higher decline of the fire resistance, compared to exposing only the columns to fire. Furthermore, the results show that the frames pushed to arrive at LS and CP levels of performance collapse in a global collapse mode laterally, whereas at the IO level of performance and fire-alone situation, the collapse mechanism is mostly local through the collapse of beams. Whilst the investigation is conducted for a certain class of portal frames, the results confirm the need for the incorporation of PEF into the process of analysis and design, and provide some quantitative measures on the level of associated effects.

Probabilistic models for curvature ductility and moment redistribution of RC beams

Hassan Baji,Hamid Reza Ronagh 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.2

It is generally accepted that, in the interest of safety, it is essential to provide a minimum level of flexural ductility, which will allow energy dissipation and moment redistribution as required. If one wishes to be uniformly conservative across all of the design variables, curvature ductility and moment redistribution factor should be calculated using a probabilistic method, as is the case for other design parameters in reinforced concrete mechanics. In this study, simple expressions are derived for the evaluation of curvature ductility and moment redistribution factor, based on the concept of demand and capacity rotation. Probabilistic models are then derived for both the curvature ductility and the moment redistribution factor, by means of central limit theorem and through taking advantage of the specific behaviour of moment redistribution factor as a function of curvature ductility and plastic hinge length. The Monte Carlo Simulation (MCS) method is used to check and verify the results of the proposed method. Although some minor simplifications are made in the proposed method, there is a very good agreement between the MCS and the proposed method. The proposed method could be used in any future probabilistic evaluation of curvature ductility and moment redistribution factors.

Post-Earthquake Fire Performance-based Behavior of Unprotected Moment Resisting 2D Steel Frames

Behrouz Behnam,Hamid Reza Ronagh 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

Post-Earthquake Fire (PEF) can lead to the collapse of buildings that are partially damaged in a prior earthquake that occurredimmediately before the fire. The majority of standards and codes for the design of structures against earthquake ignore the possibilityof PEF and thus buildings designed with those codes fail prematurely when subjected to PEF. A sequential analysis based onFEMA356 is performed here on the Immediate Occupancy (IO), corresponding to a structure designed as school occupancy, and LifeSafety (LS) performance levels, corresponding to a structure designed as reside ntial occupancy, of two steel moment resistingframes. These frames are first subjected to an earthquake load with the PGA of 0.35g. This is followed by a fire analysis, using boththe ISO834 model and the Natural fire model. The time it takes for the structure weakened by the earthquake to collapse under fire isthen calculated. As a point of reference, fire only analyses are also performed for the undamaged structures. The results show thatearthquake weakened structures are more vulnerable to fire than undamaged structures. The results also show that both fire resistanceand PEF resistance of the frame designed as school are more than the frame designed as residential. Whilst the investigation is for acertain class of structures (steel moment resisting frames, 5 stories), the results confirm the need for the incorporation of PEF in theprocess of analysis and design and provides some quantitative measures on the level of associated effects.

Seismic risk assessment of deficient reinforced concrete frames in near-fault regions

Cao, Vui Van,Ronagh, Hamid Reza,Baji, Hassan Techno-Press 2014 Advances in concrete construction Vol.2 No.4

In many parts of the world, reinforced concrete (RC) buildings, designed and built in accordance with older codes, have suffered severe damage or even collapse as a result of recent near-fault earthquakes. This is particularly due to the deficiencies of most of the older (and even some of the recent) codes in dealing with near fault events. In this study, a tested three-storey frame designed for gravity loads only was selected to represent those deficient buildings. Nonlinear time history analyses were performed, followed by damage assessment procedures. The results were compared with experimental observation of the same frame showing a good match. Damage and fragility analyses of the frame subjected to 204 pulse-type motions were then performed using a selected damage model and inter-storey drifts. The results showed that the frame located in near-fault regions is extremely vulnerable to ground motions. The results also showed that the damage model better captures the damage distribution in the frame than inter-storey drifts. The first storey was identified as the most fragile and the inner columns of the first storey suffered most damage as indicated by the damage index. The findings would be helpful in the decision making process prior to the strengthening of buildings in near-fault regions.

Investigating the effect of bond slip on the seismic response of RC structures

Fallah, Mohammad Mehdi,Shooshtari, Ahmad,Ronagh, Hamid Reza Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.5

It is reasonable to assume that reinforced concrete (RC) structures enter the nonlinear range of response during a severe ground motion. Numerical analysis to predict the behaviour therefore must allow for the presence of nonlinear deformations if an accurate estimate of seismic response is aimed. Among the factors contributing to inelastic deformations, the influence of the degradation of the bond slip phenomenon is important. Any rebar slip generates an additional rotation at the end regions of structural members which are not accounted for in a conventional analysis. Although these deformations could affect the seismic response of RC structures considerably, they are often neglected due to the unavailability of suitable models. In this paper, the seismic response of two types of RC structures, designed according to the Iranian concrete code (ABA) and the Iranian seismic code (2800), are evaluated using nonlinear dynamic and static analyses. The investigation is performed using nonlinear dynamic and static pushover analysis considering the deformations due to anchorage slip. The nonlinear analysis results confirm that bond slip significantly influences the seismic behavior of RC structure leading to an increase of lateral deformations by up to 30% depending on the height of building. The outcomes also identify important parameters affecting the extent of this influence.

Effect of Inverted-V Bracing on Retrofitting Against Progressive Collapse of Steel Moment Resisting Frames

Farshad Hashemi Rezvani,Mohammad Ali Mohammad Taghizadeh,Hamid Reza Ronagh 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.3

The effect of inverted-V bracing on enhancing progressive collapse resistance of steel Moment Resisting Frames (MRF) were investigated in this study. A series of nonlinear static and dynamic analyses were performed to determine the resistance of four generic MRFs retrofitted by ten inverted-V bracing element. These structures were subjected to an exterior column loss and had a different number of stories and span lengths in order to study the effect of these variations on the structural response. Both force-controlled and deformation-controlled actions were implemented to determine if the column loss would lead to a failure progression. Results showed that structural configuration affects the structural resistance against failure progression and hence the appropriate brace element to retrofit it. Also, it was shown that for the studied 4-story frames, by increasing the span length by 20%, the structural resistance decreases by 42% on average. Finally, it was observed that by decreasing the span length, the Dynamic Increase Factor (DIF) suggested by the UFC, will lead to underestimating the required cross-sectional area of the brace for strengthening the unbraced structures.

Investigating the effect of bond slip on the seismic response of RC structures

Mohammad Mehdi Fallah,Ahmad Shooshtari,Hamid Reza Ronagh 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.5

It is reasonable to assume that reinforced concrete (RC) structures enter the nonlinear range of response during a severe ground motion. Numerical analysis to predict the behaviour therefore must allow for the presence of nonlinear deformations if an accurate estimate of seismic response is aimed. Among the factors contributing to inelastic deformations, the influence of the degradation of the bond slip phenomenon is important. Any rebar slip generates an additional rotation at the end regions of structural members which are not accounted for in a conventional analysis. Although these deformations could affect the seismic response of RC structures considerably, they are often neglected due to the unavailability of suitable models. In this paper, the seismic response of two types of RC structures, designed according to the Iranian concrete code (ABA) and the Iranian seismic code (2800), are evaluated using nonlinear dynamic and static analyses. The investigation is performed using nonlinear dynamic and static pushover analysis considering the deformations due to anchorage slip. The nonlinear analysis results confirm that bond slip significantly influences the seismic behavior of RC structure leading to an increase of lateral deformations by up to 30% depending on the height of building. The outcomes also identify important parameters affecting the extent of this influence.

Load-deflection analysis prediction of CFRP strengthened RC slab using RNN

Razavi, S.V.,Jumaat, Mohad Zamin,El-Shafie, Ahmed H.,Ronagh, Hamid Reza Techno-Press 2015 Advances in concrete construction Vol.3 No.2

In this paper, the load-deflection analysis of the Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (RC) slab using Recurrent Neural Network (RNN) is investigated. Six reinforced concrete slabs having dimension $1800{\times}400{\times}120mm$ with similar steel bar of 2T10 and strengthened using different length and width of CFRP were tested and compared with similar samples without CFRP. The experimental load-deflection results were normalized and then uploaded in MATLAB software. Loading, CFRP length and width were as neurons in input layer and mid-span deflection was as neuron in output layer. The network was generated using feed-forward network and a internal nonlinear condition space model to memorize the input data while training process. From 122 load-deflection data, 111 data utilized for network generation and 11 data for the network testing. The results of model on the testing stage showed that the generated RNN predicted the load-deflection analysis of the slabs in acceptable technique with a correlation of determination of 0.99. The ratio between predicted deflection by RNN and experimental output was in the range of 0.99 to 1.11.