Accidental or premeditated explosions have detrimental effects on the infrastructure near the center of explosion and pose major threats to human life. Thus, research is currently underway to study the effects of explosions on infrastructure systems with the ultimate goal of minimizing infrastructure damage and saving lives. Because reinforced concrete is the most common building material used in blast-resistant infrastructure design and construction, understanding the effect of blast loads on reinforced concrete components is essential to reaching this goal. The prevailing design philosophy for blast-resistant structures is energy dissipation through reinforcement yielding (ductility) and large bending deformations without the incidence of nonductile failure modes such as shear and bond. However, information regarding the bond behavior and strength of steel reinforcement-concrete bonds under blast loads is rather scant; therefore, this paper reports on an experimental program designed to investigate the strain rate effect on steel reinforcement-concrete bond. Reinforced concrete beams longitudinally reinforced with 15M, 20M, or 25M were tested in a shock tube under simulated blast loading. The test results show that high strain rate increases the steel reinforcement-concrete bond strength and thus, that the static load development lengths of these bars are adequate for developing their dynamic yield strengths at high strain rate. The dynamic increase factor for bond stress is determined to be 1.11 for 15M, 2.24 for 20M, and 3.68 for 25M bar. (C) 2015 American Society of Civil Engineers.

In this study, 13 typical wide-flange steel columns, each carrying an axial load equal to 25% of its axial capacity, are field tested using live explosives, involving charge size of 50 to 250 kg of ammonium nitrate/fuel oil (ANFO) and ground stand-off distance of 7.0 to 10.3 m. The reflected pressure time histories, time-dependent displacements, accelerations, and strains of the columns are measured, and their postblast damages and failure modes are reported. Maximum deformations, vibration periods, strain-rate, and contributing modes in the dynamic response of the columns are compared to those of companion steel beams (without axial load) tested in the same setup. Results show that columns that exhibit elastic response, due to the elongation of the column vibration period caused by the axial load, the lateral deformation caused by blast load is reduced rather than magnified by the axial load. The axial-bending interaction, or P-delta effect, may be neglected for steel columns with axial load up to 25% of their axial capacity, provided the column response remains within the elastic range-but if it crosses into the plastic range, the interaction cannot be ignored. (C) 2014 American Society of Civil Engineers.

The increasing tendency to use urban civilian buildings for military purposes prompts the need for the assessment of their blast resistance. Many of these buildings are made of reinforced concrete ( RC). Popular tools available for the assessment of existing RC structures in practice include guidelines and design standards, technical manuals and specialised software. These tools include certain assumptions based on scarcely available test data, as historically they were collected for military purposes. Efforts to transfer this knowledge from military to civilian applications are relatively recent and need be corroborated by further testing and numerical analysis. The objective of this paper is to present the results of field tests on full-scale RC members to check the validity of a number of assumptions routinely made in current numerical/analytical models. The data captured during the tests, including reflected pressure and member displacements, are compared with results of empirical and numerical models, in order to gauge the robustness and accuracy of the assumptions underpinning these models. Finally, recommendations are made for an expedient assessment of existing buildings based on simple methodologies.

A Single-Degree-of-Freedom (SDOF) model is used to determine the effect of axial load on column strength and stability during a blast event. The model, which accounts for the axial load–bending interaction (P–δ effect) and strain rate effect on the column dynamic response, is validated by comparing its results with experimental data from blast tests on full scale steel columns and with the results of the finite element software LS-DYNA. Maximum displacements and moments obtained from SDOF analysis are also compared with the results of the interaction formulas recommended by the Unified Facilities Criteria (UFC 3-340-02) design manual for steel structures. It is shown that the UFC method overestimates the column capacity for ductility ratios μ greater than one, irrespective of the axial load to Euler elastic buckling load ratio (P/Pe). Also for P/Pe>0.5, even if μ<1.0, the UFC method still overestimates the actual column capacity. For dealing with this problem in practical applications, non-dimensional beam column curves are developed to include the effects of the blast load and column properties on both its strength and stability.

The selection of seismic motions is one of the most important issues for the time-history analysis of buildings. This paper discusses four different methods for obtaining spectrum-compatible acceleration time histories (i.e., accelerograms) of seismic motions. Based on these methods, four sets of accelerograms compatible with the design spectrum for Vancouver were selected for this study. These included (i) scaled real accelerograms, (ii) modified real accelerograms, (iii) simulated accelerograms, and (iv) artificial accelerograms. The selected sets were used as excitation motions in the nonlinear analysis of three reinforced concrete frame buildings designed for Vancouver. The buildings included a 4-storey, a 10-storey, and a 16-storey building, which can be considered representative of low-rise, medium-rise, and high-rise buildings, respectively. The storey shears, interstorey drifts, and curvature ductilities for beams and columns obtained from the analysis were used for the evaluation of the effects of the selected sets on the responses of the buildings. Based on the results from the analysis, scaled real accelerograms are recommended for use in time-history analysis of reinforced concrete frame buildings.

The re-centering phenomenon of superelastic Shape Memory Alloy (SMA) reinforced concrete is a unique characteristic that is appealing for structural applications, along with the ability to respond with stable hystereses and achieve similar strength and ductility to concrete reinforced with conventional deformed bars. The objective of this study was to investigate the structural performance of superelastic SMA reinforced concrete and to develop a preliminary constitutive model applicable to nonlinear finite element algorithms. Seven simply supported flexure-critical concrete beams, reinforced with either SMA bars in the critical region or conventional deformed reinforcement, were subjected to monotonic, cyclic, and reverse cyclic loading. The experiment results demonstrated the superior capacity of the SMA beams to recover inelastic displacements. The SMA beams sustained displacement ductility and strength capacity comparable to the conventional beams. Crack widths and crack spacing were larger in the SMA beams; however, upon removal of load, the crack openings were recovered. Energy dissipation was lower in the SMA beams, particularly when subjected to reverse cyclic loading. The constitutive model based on a trilinear backbone envelope response and linear unloading and reloading rules provided satisfactory simulations. (C) 2013 Elsevier Ltd. All rights reserved.

Results of an experimental study on the bond performance of deformed steel rebars in concrete made with coarse recycled concrete aggregate (RCA) are presented. The distinctive feature of the study is the new mix proportioning method for RCA concrete that results in the strength to elastic modulus ratio (f'(c)/E-c) similar to a conventional concrete having the same amount of total mortar and coarse aggregate. In this method, the properties and volume fractions of natural aggregate and residual mortar in RCA are quantitatively included as part of the total aggregate and total mortar content of the RCA concrete. Twelve beam-end bond specimens were prepared and tested according to ASTM A944-99 standard. The test variables comprised mix proportioning method, bar size, and aggregate type. The results showed that the bond strength between the reinforcing steel bars and the RCA concrete proportioned by the new method is comparable to their bond strength with regular concrete but 18% to 33% higher than their strength with RCA concrete proportioned by conventional methods.

This paper presents detailed analysis of the results of field tests on 13 full scale wide flange steel beams subjected to blast loads generated by the detonation of up to 250 kg of ANFO explosive. The experimental results are analyzed using an equivalent Single-Degree-of-Freedom (SDOF) model of a beam, which includes material nonlinearity and strain rate effects. To account for strain rate effect on beam stiffness and strength, its full moment-curvature response is determined by dividing its cross-section into a number of layers and a strain rate-dependent stress-strain relationship, based on the Cowper-Symonds strain rate model, is used to capture the nonlinear stress distribution over the section. To determine the effects of higher modes of vibration and the variation of beam mechanical properties along its length on its dynamic response, the test beams are also analyzed using a Multi-Degree-of-Freedom (MDOF) model involving beam finite elements. Each element has two nodes and three degrees of freedom and is again divided into a number of layers to capture the strain rate effect and nonlinear stress distribution over its depth. The predicted displacements and strains by the two models are compared with the corresponding experimental data and the results show that for the given beams, the time-dependant deformations, internal forces, and moments can be adequately predicted by either model because the first mode of vibration is found to dominate their response; however, the use of a constant strain rate through the so-called Dynamic Increase Factor (DIF) can lead to highly conservative estimate of the actual strength of such members. (C) 2011 Elsevier B.V. All rights reserved.

Abou-Zeid, Badr; El-Dakhakhni, Wael; Razaqpur, Ghani and Foo, Simon 1 PhD, Senior Engineer, Structural Department, SNC-Lavalin group, Cairo, Egypt. badr.abouzeid@snclavalin.com 2 PhD, Martini, Mascarin and George Chair in Masonry Design, McMaster University, Canada. eldak@mcmaster.ca 3 PhD, Professor, McMaster University, Hamilton, L8S 4L7, Ontario, Canada. razaqpu@mcmaster.ca 3 PhD, Senior Engineer, Real Property Branch, Public Works & Government Services, Canada. simon.foo@pwgsc.gc.ca

Shape Memory Alloys (SMAs) are a relatively new group of alloys that have emerged as potential alternative reinforcement in concrete structures. Shape memory alloys have the ability to sustain large deformations and to return to their original undeformed shape upon removal of stress (superelastic SMA) or with the application of heat (shape memory effect). In addition, SMA reinforced concrete can dissipate energy through hysteretic damping. The unique properties of SMAs can address shortcomings of conventional deformed reinforcing bars, specifically in controlling permanent strains, which is the most appealing characteristic, and, in theory, could lead to restoring a structural component after significant loading. The objective of this paper is to highlight the applicability and practicality of superelastic SMAs as alternative reinforcement in structural applications. Advantages and disadvantages of superelastic SMA reinforced concrete through experimental studies of bare SMA rods and reinforced concrete beams subjected to cyclic loading will be discussed.

Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.

The applicability of some major concrete design standards and other pertinent methods to calculate the concrete contribution to the shear resistance of reinforced recycled concrete (RRC) beams without stirrups is investigated. Results of a relatively comprehensive experimental program are used to compare the actual shear strength of the tested beams with their corresponding predicted values. The concrete mixes for the RRC beams were proportioned by the so-called Equivalent Mortar Volume (EMV) method. The method is predicated on the fact that recycled concrete aggregate (RCA) is a composite material, comprising mortar and natural aggregate, and the volumetric content and properties of each phase must be quantitatively accounted for when proportioning concrete mixes containing RCA. The test variables included in the test program are shear-span/depth ratio, beam size, RCA source, and coarse aggregate type. The results show that the shear capacity of a RRC beam is comparable, or sometimes superior, to that of a companion beam made of conventional concrete. The analyses performed in the current investigation show, contrary to previous findings, that existing shear design methods, such as the ACI and CSA codes methods, are applicable to RRC beams, provided the EMV method of mix design is used.

This is the second of two companion papers on improved intensity measures of strong seismic ground motions for use in probabilistic seismic demand analysis of reinforced concrete frame buildings. The first paper discusses the development of improved intensity measures. This paper describes the application of the developed intensity measures in probabilistic seismic demand analysis. The application is illustrated on the three reinforced concrete frame buildings (4, 10, and 16-storey high) that were used in the first paper. This involved computations of the seismic responses of the structures and the seismic hazard using the improved intensity measures. The response and the hazard results were then combined by means of probabilistic seismic demand analysis to determine the mean annual frequencies of exceeding specified response levels due to future earthquakes (i.e., the probabilistic seismic demands). For the purpose of comparison, probabilistic seismic demand analyses were also conducted by employing the spectral acceleration at the fundamental structural periods (Sa(T1)) as an intensity measure, which is currently the most used in practice. It was found that the use of the improved intensity measures results in significantly lower seismic demands relative to those corresponding to the intensity measure represented by Sa(T1), especially for long period structures.

In this study, the dynamic response of typical wide-flange steel beams was experimentally evaluated under blast loading. A total of 13 beams were field tested using live explosives, where the charge size ranged from 50 to 250 kg of ammonium nitrate-fuel oil mixture, and the ground stand-off distance was from 7.0 to 10.3 m. Blast wave characteristics, including incident and reflected pressures, were recorded. In addition, time-dependent displacements, accelerations, and strains at different locations along the steel members were measured, and the postblast damage and mode of failure of the test specimens were observed. The blast load characteristics were compared with those obtained using the Technical Manual UFC 3-340-02 results. The displacement response results were used to validate the results obtained from a nonlinear dynamic analysis based on a single degree-of-freedom (SDOF) model. Results showed that the UFC 3-340-02 pressure predictions compare reasonably well with the measured pressure in the positive phase in terms of both the peak pressure and overall time variations. The SDOF model predicted the maximum displacements of beams in the elastic range reasonably well, but it overestimated them in the plastic range.

This is the first of two companion papers on improved intensity measures of strong seismic ground motions for use in probabilistic seismic demand analysis. It describes the formulation and the development of new intensity measures. The second paper illustrates the application of the developed intensity measures in probabilistic seismic demand analysis. The development of the intensity measures was based on investigations of the seismic responses of three reinforced concrete frame buildings (4, 10, and 16-storey high) designed for Vancouver. The buildings were subjected to a selected set of seismic motions scaled to different intensity levels. Maximum interstorey drifts obtained from nonlinear dynamic analyses were used as response parameters. Based on the results from the analyses, two intensity measures are proposed: one for short- and intermediate-period buildings, and another one for long-period buildings. The proposed intensity measures are superior compared to that represented by the spectral acceleration at the fundamental building period (Sa(T1)), which is currently the most widely used intensity measure in probabilistic seismic demand analysis.

This paper describes results from a study on the dynamic behaviour of the Confederation Bridge due to seismic loads. For the purpose of the seismic analysis of the bridge, a finite element model was developed using three-dimensional (3D) beam elements. The model was calibrated using measured data of the bridge vibrations during a dynamic load test. Dynamic analyses were conducted by subjecting the model to selected seismic ground motions representative of the expected motions at the bridge location. The bending moments and displacements obtained from the analyses were used for the seismic evaluation of the bridge. It was found that the seismic effects considered in the design are appropriate for the required safety during the service life of the bridge.

Because of changes in functional or security requirements, many new or existing buildings are now required to resist blast loads. New buildings can be designed and constructed to resist defined blast loads. Existing buildings, on the other hand, would have to rely on a risk assessment to determine both its vulnerability to blast effects and the necessary measures to mitigate the unacceptable blast effects. A rapid screening methodology has been developed for conducting a preliminary assessment of buildings against external blast effects. The methodology accounts for the threat, the vulnerability of the building, the consequence of an event and the risk, which is the product of the threat and the consequence. The rapid screening methodology has been applied to several buildings and the results are reasonable. This paper presents the rapid screening methodology and its application to two federal buildings in Canada.