Hamid Reza Ronagh

Experimental Investigation of an Appropriate Anchorage System for Flange-Bonded Carbon Fiber-Reinforced Polymers in Retrofitted RC Beam-Column Joints

External application of fiber-reinforced polymers (FRPs) for the seismic retrofit/repair of reinforced concrete (RC) beam-column joints has been extensively investigated in the last decade. However, the majority of the suggested FRP schemes follow the application of the composite sheets on the webs of the beam and the joint core which would be impeded in real three-dimensional structures due to the presence of cross beams and slabs. In addition, upgrading code-compliant RC joints using a practical FRP scheme needs to be scrutinized in detail. A desirable retrofitting scheme for this type of joints may follow the application of composite sheets on the top and bottom sides (flanges) of the beam and columns aimed at increasing the flexural strength of beam-column joints. However, the major issue of concern for a flange-bonded FRP is providing adequate development length from the critical section to transfer the FRP tensile forces from beam to columns and vice versa. To overcome this concern, a novel anchorage system for flange-bonded carbon FRP (CFRP) is developed in this study and its efficiency is evaluated through a comprehensive experimental program. In total, nine small-scale (1/2.85) beam-column test specimens, including two control specimens, one damaged specimen, and six retrofitted specimens were considered. Both monotonic and cyclic loading regimes were implemented to estimate, albeit approximately, the seismic responses of the test specimens. The load-carrying capacity, initial stiffness, displacement ductility, and dissipated energy of beam-column joint subassemblies are compared before and after the application of the CFRP retrofits. The results showed a remarkable improvement in the load-carrying capacity and elastic stiffness of CFRP-retrofitted specimens, thus confirming the efficiency of the suggested anchorage system. In addition, and subject to specific circumstances, the plastic hinge can also be relocated away from the beam-column interface.

Modification of advanced programmatic risk analysis and management model for the whole project life cycle's risks

The advanced programmatic risk analysis and management model (APRAM) is one of the recently developed methods that can be used for risk analysis and management purposes considering schedule, cost, and quality risks simultaneously. However, this model considers those failure risks that occur only over the design and construction phases of a project’s life cycle. While it can be sufficient for some projects for which the required cost during the operating life is much less than the budget required over the construction period, it should be modified in relation to infrastructure projects because the associated costs during the operating life cycle are significant. In this paper, a modified APRAM is proposed, which can consider potential risks that might occur over the entire life cycle of the project, including technical and managerial failure risks. Therefore, the modified model can be used as an efficient decision-support tool for construction managers in the housing industry in which various alternatives might be technically available. The modified method is demonstrated by using a real building project, and this demonstration shows that it can be employed efficiently by construction managers. The Delphi method was applied in order to figure out the failure events and their associated probabilities. The results show that although the initial cost of a cold-formed steel structural system is higher than a conventional construction system, the former’s failure cost is much lower than the latter’s

An Analytical Solution for the Elastic Lateral-Distortional Buckling of I-section Beams

Lateral-distortional buckling may occur in I-section beams with slender webs and stocky flanges. A computationally efficient method is presented in this paper to study this phenomenon. Previous studies on distortional buckling have been on the use of 3rd and 5th order polynomials to model the displacements. The present study provides an alternative way, using Fourier Series, to model the behaviour. Beams of different cross-sectional dimensions, load cases and restraint conditions are examined and compared. The accuracy and versatility of the method are verified by calibrating against the results of other published studies. The present method is believed to be a simple and efficient way of determining the buckling load and mode shapes of I-section beams that are susceptible to lateral-distortional buckling modes.

Numerical Investigation on the Hysteretic Behavior of RC Joints Retrofitted with Different CFRP Configurations

The strengthening of beam-column joints in RC structures is considered an effective approach for improving their seismic resistance and overall performance. This paper presents a numerical investigation into the effectiveness of carbon fiber-reinforced polymer (CFRP) sheets in enhancing the seismic performance of RC joints under combined axial and cyclic loads. For this purpose, a case-study joint subassemblage was retrofitted using three different retrofitting configurations (L-shaped, web bonded, and flange bonded), all commonly used for external strengthening with composite materials. Following the verification of the nonlinear numerical model against the existing experimental data, the analysis outcomes of the retrofitted specimens were compared with those of the control specimen in terms of the tip beam load distribution versus tip beam displacement, energy dissipation, and plastic hinge relocation. Compared with the results of the original joint, the results of the retrofitted joints confirmed an improved load-carrying capacity for all strengthening schemes. However, some configurations led to a decrease in the ductility and dissipated energy. It was shown that the L-shaped and flange-bonded retrofitting schemes could relocate the plastic hinge from the column face toward the beam. This represents a good outcome because it can potentially eliminate the possibility of joint core brittle failure.

Probabilistic Design Models for Ultimate Strength and Strain of FRP-Confined Concrete

AbstractThis paper presents a probabilistic procedure for deriving design models for the ultimate strength and strain of fiber–reinforced-polymer (FRP)-confined concrete. First, a large database of axial compression tests performed on circular FRP-confined concrete specimens is collected for calibrating an ultimate strength model, based on the Drucker-Prager criterion, and an ultimate strain model, based on the ultimate dilation rate. The database is also employed for deriving a probabilistic model for the FRP strain efficiency factor. The calibrated models, though simple, show superior performance over some of the models in the literature. Then, using the Central Limit Theorem and considering uncertainty in the mechanical properties of the concrete and FRP material as well as their correlation, analytical probabilistic design models for the ultimate strength and strain of FRP-confined concrete are derived. These models can be used in the design and reliability analysis of FRP-confined columns.

A study on the effect of sequential post-earthquake fire on the performance of reinforced concrete structures

Purpose – Post-earthquake fire (PEF) can lead to a rapid collapse of structures partially damaged by earthquake. As there is almost no established PEF provisions by codes and standards, PEF investigations are therefore needed for those buildings. The paper aims to discuss these issues. Design/methodology/approach – A non-linear PEF analysis comprises three steps, which are the application of gravity loads, earthquake loads and then fire loads. As a fire generally initiates on one floor and then spreads to other floors, applying a sequential fire is more realistic than applying a concurrent fire on several floors. Hence, in this study, the fire is applied sequentially to the floors with a time delay. Findings – The results indicate a substantial reduction in the resistance of the damaged frame when subjected to PEF. In addition, the results of applying the PEF sequentially is more realistic than the concurrent fire. Research limitations/implications – It was better to perform an experimental test to have a...

A post-earthquake fire factor to improve the fire resistance of damaged ordinary reinforced concrete structures

Post-earthquake fire (PEF) is considered as one of the most problematic potentially possible disasters in urban areas, as it may result in a conflagration. Most standards and criteria, however, ignore the possibility of fire after earthquake and therefore, majority of conventional buildings are not designed to resist thermal loading after an earthquake. Thus, there is high likelihood of rapid collapse for those buildings damaged partially after an earthquake, which are subjected immediately to a following fire. An investigation based on sequential analysis inspired by FEMA356 is performed in this paper on two RC frames; three and five stories at the Life-Safety performance level and designed to the ACI 318-08 code after they are subjected to a spectral PGA of 0.35g. This is followed by a five-hour fire analysis of the weakened structures, from which the time it takes for the damaged structures to collapse is calculated. As a point of reference, the fire resistance is also determined for undamaged structures and before the occurrence of earthquake. The results show that the structures previously damaged by the earthquake and exposed to PEF are more vulnerable than those that are not damaged. A CPEF greater than 1 is then introduced as a function of fire extinguishing or evacuating time that can be multiplied by the base shear at the time of design in order to increase members sizes and thus improve the PEF resistance. Whilst the investigation is for a certain class of structures (ordinary buildings, intermediate reinforced concrete structure, three and five stories), the results confirm the need for the incorporation of post earthquake fire in the process of analysis and design, and provides some quantitative measures on the level of associated effects.

Sagging and Hogging Strengthening of Continuous Unbonded Posttensioned HSC Beams by NSM and EBR

Continuous unbonded posttensioned concrete beams might require strengthening to cope with higher demands. Strengthening with carbon-fiber-reinforced plastics (CFRP) is a viable option; however, because of the limited number of studies in this area and lack of experimental data, the guidelines covered only bonded prestressed concrete members, in particular when these are made from high-strength concrete (HSC). This paper reports on the results of an experimental investigation on the flexural behavior of continuous unbonded posttensioned HSC beams strengthened using CFRP. In this application, the CFRP is either externally bonded reinforcement (EBR) or internally near-surface mounted (NSM) in both hogging and sagging regions. The results show that both service and ultimate states of continuous unbonded posttensioned concrete beams were considerably improved by CFRP strengthening, and also that the efficiency of the NSM method is greater than that of the EBR method, especially in crack propagation and ultimate load.

Numerical Evaluation of the Post-Earthquake Fire Resistance of CFRP-Strengthened Reinforced Concrete Joints based on Experimental Observations

This article describes experimental and numerical studies on the structural resistance of two reinforced concrete beam-column joints. While both specimens are of similar configurations as for geometry, amount and type of steel reinforcement and concrete strength, the second is strengthened by means of carbon fibre-reinforced polymer (CFRP) at the vicinity of the joint in order to relocate the plastic hinge away from the column extremity towards the beam. Both specimens are subjected to a cyclic load followed by a generalised exponential fire curve, which implicitly represents a post-earthquake fire (PEF). The PEF resistance of the specimens subjected to various damage levels such as immediate occupancy (IO), life safety (LS) and collapse prevention (CP) is then evaluated based on finite element analysis. The results show that while the fire resistances of the original specimen subjected to LS and CP damage levels are about 32 and 15 min, respectively, they increase in the CFRP-strengthened specimen to about 43 and 23 min, respectively. This represents a 25% increase at LS level and a 35% increase at CP level.

Performance-Based Vulnerability Assessment of Multi-Story Reinforced Concrete Structures Exposed to Pre- and Post-Earthquake Fire

Post-earthquake fire can potentially bring about much more damage than the earthquake itself. Performing a vulnerability assessment for a structure that has already sustained damage in an earthquake and is then exposed to fire is therefore of importance. This paper describes a performance-based investigation in which applied loads to a structure are appropriately quantified. To do so, a sequential structural analysis is performed on the Life Safety performance level of a three-story reinforced concrete frame selected from a building. For the analysis to be more realistic, the slab is also included in the frame analysis through the concept of effective length. The frame is first subjected to an earthquake load with the PGA of 0.30 g followed by a fire analysis, using the ISO834 fire curve and the iBMB fire curve. The time needed for the structure weakened by the earthquake to collapse under fire is then calculated. As a benchmark, fire-only analysis is also performed for the undamaged frame. Moreover, the effect of thermal spalling is considered in the slabs. The selected frame is evaluated under various failure criteria such as load capacity, displacement, and rate of displacement. The results show that no failure is observed when the frame is exposed to fire alone, either when using the ISO curve or the iBMB curve under various failure criteria. It is also shown that while the PEF resistance based on load capacity criteria under the ISO curve is around 120 minutes, it reduces to about 95 min under the iBMB curve. However, considering the rate of deflection failure criteria, the PEF resistance is around 103 min and 75 min under the ISO and the iBMB curves, respectively. It is then concluded that in the PEF analysis, the iBMB curve is more compatible with the concept of performance-based design than the ISO curve is.