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.
This paper presents a summary of experimental research on the performance of blast-resistant window anchors and the development of a design procedure for the anchors. The experimental results, obtained from forty-six window tests conducted under simulated blast loading using a shock tube are reported. Two analysis procedures that were developed for anchor design are described. The first procedure involves a two-degree-of-freedom dynamic analysis. The second procedure involves a single degree of freedom analysis that can be implemented manually. The development of both methods is presented for the anchorage design of windows subjected to blast loads.
Champlain Bridge, which stood from 1962 to 2019, was a significant highway structure spanning the St. Lawrence River and St. Lawrence Seaway. It was constructed using concrete incorporating an alkali–silica reactive aggregate. Decommissioning of the structure presented a unique research opportunity to investigate how damage owing to alkali–silica reaction (ASR) developed in a concrete member with various levels of restraint. Following decommissioning of the pier cap, cores were extracted longitudinally from a number of restraint locations within the member (i.e. top, middle and bottom regions) and investigated using a multi-level assessment protocol through microscopic (i.e. damage rating index) and mechanical (i.e. stiffness damage test) test procedures. Cracking travelling parallel to the coring direction in the extracted cores (i.e. parallel to main reinforcement) was observed in all regions, indicating an influence of restraint conditions on ASR-induced development. Moreover, increased expansion due to ASR, similar to reference cores extracted transversally, was identified in cores extracted from the highest reinforcement region, while cores from the middle and bottom regions displayed a reduced deterioration.
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Lateral steel in columns is generally required for shear resistance, confinement of concrete and prevention of buckling of longitudinal bars. This paper is limited to the design of lateral steel for confinement and bar buckling only. The provisions of the ACI 318-89 code (1989) related to this area are critically examined and changes are suggested to these provisions to make the design more rational. Both the tied and the spirally reinforced columns are considered and seismic as well as non-seismic design provisions are discussed.
It has been shown over the past three decades that fiber reinforced polymer (FRP) composite tubes offer an attractive alternative to conventional confinement reinforcement to enhance strength and deformability of concrete columns. Concrete-filled FRP tube (CFFT) columns have been shown to exhibit highly ductile behavior under simulated seismic loading, making them suitable for use in earthquake-resistant construction. For the design of CFFT columns in new construction there is need for a rational procedure that enables the prediction of lateral drift capacities of these columns. This paper presents such a procedure for displacement-based design of circular and square CFFT columns. The approach incorporates influences of experimentally observed confinement parameters while also including axial load level and lateral drift capacity as design variables. The expression derived as part of the proposed design procedure has been validated using available experimental data, and it has been shown that the predicted capacities are in good agreement with the experimental results.
Previous earthquakes have clearly demonstrated that the damage to operational and functional components of buildings usually cause more injuries, fatalities, and property and financial loss than those inflicted by structural damage. Operational and functional components of a building include architectural components, mechanical and electrical equipment, and building contents. An important step towards ensuring the safe design of operational and functional components of buildings is to develop floor design response spectra. This constitutes the scope of the current research program described in this paper. A total of 6 buildings, consisting of 5, 10 and 15-story frame buildings were designed and analyzed to establish floor response spectra. The buildings were designed for Ottawa and Vancouver representing Eastern and Western Canadian seismicity. Fifteen artificially generated earthquake records (accelerograms) were used for each structure, compatible with the Uniform Hazard Response Spectra specified in the 2005 edition of the National Building Code of Canada. It was observed that the response amplifications relative to ground excitations varied from floor to floor, and were frequency dependent. Generally, the higher floors showed higher amplification with differences in spectra between the floors being more pronounced in low-rise buildings, as compared to medium and high-rise buildings. The acceleration floor response spectra for individual floors are presented in the paper with details of the analyses that led to their developments. Recommendations are made for design floor response spectra for reinforced concrete frame buildings in Canada.
This paper presents the results of an investigation of the dynamic behavior of a reinforced concrete frame that was strengthened by a buckling-restrained brace (BRB). The behavior of this frame was benchmarked against a control frame without strengthening. Both frames were tested concurrently on a shake table using the acceleration time-history record from the 1995 Kobe earthquake. The BRB-strengthened frame was additionally subjected to two levels of a synthetic time-history record to observe its behavior under severe ground shaking. The stiffness of the BRB-strengthened frame increased by 70% relative to the control frame. Furthermore, the cracked BRB-strengthened frame retained approximately 80% higher stiffness compared with the cracked control frame at an applied peak ground acceleration (PGA) of 0.679g. Conversely, the lateral story drift of the BRB-strengthened frame was 46% less compared with the control frame at this level of acceleration. The control frame failed by concrete crushing at base of the columns at PGA of 0.679g after yielding of the longitudinal reinforcing bars. The dissipation of hysteretic energy for the control frame reached a maximum at 0.435g, whereas the BRB-strengthened frame exhibited high strength capacity without any marked change in stiffness at 0.679g.
A reconnaissance was conducted in Thailand to investigate the effects of the 26 December 2004 tsunami on buildings, bridges, and other physical infrastructure. It was observed that nonengineered reinforced concrete buildings, low-rise timber frames, and unreinforced masonry walls suffered extensive damage from hydrodynamic pressures generated by the tsunami. A large number of nonengineered reinforced concrete frame buildings experienced partial or total collapse, while well-designed engineered structures survived the tsunami with little or no damage. Specific observations made during the reconnaissance indicate the engineering significance of the disaster.
This paper presents two different approaches to model corrosion-induced crack propagation in reinforced concrete (RC) structures. Both approaches are based on a thick-walled cylinder analogy, in which the concrete cover is subjected to the internal pressure generated by the growth of corrosion products, and both consider rust compressibility and rust diffusion into cracks. The first approach is solved numerically using finite differences to model the post-cracking softening behaviour of concrete in tension. The second approach idealises the concrete cover as either a brittle elastic or an elastoplastic material, so that it may be solved using a closed-form solution. The results obtained using each approach are compared against each other as well as against published experimental results. A parametric investigation of the influence of several variables on the results provided by the modelling approaches is also presented. The experimental data found in the literature showed reasonable agreement with predictions from the numerical and elastoplastic (analytical) models.
Abstract Corrosion of reinforcing steel in reinforced concrete (RC) infrastructure is one of the most concerning durability problems affecting its serviceability and ultimate capacity in North America. The rise of greenhouse emissions in recent decades and the use of de‐icing salts during the winter increase the potential risk of corrosion. Furthermore, global warming could lead to higher freeze–thaw cycles (FTC) frequency in cold regions. The combined effects of corrosion and frost damage tend to affect aging RC infrastructure's structural performance and service life. The present study adopts comprehensive reinforcement corrosion and frost damage models from the literature and proposes a stage‐based damage analysis scenario. Three‐dimensional nonlinear finite element analyses using the commercially available finite element program DIANA are conducted to evaluate the structural performance of RC bridge piers under the synergetic effects of FTCs, corrosion, and service load during their service life. The proposed methodology for each damage mechanism is assessed by comparison with available experimental data from the literature. The synergetic effects cannot be validated because there is no data, but the methodology highlights the deterioration rate at which several mechanisms acting at the same time can affect the structural performance of these members.
Two concrete deck slabs extracted from a Canadian bridge have been evaluated using non-destructive testing (NDT), followed by destructive testing. Throughout its service life, the bridge experienced harsh environmental conditions with frequent freeze-thaw cycles, hot and humid summers, and the use of de-icing salts during winters. This study presents the preliminary results of an exhaustive condition assessment of two prestressed concrete slab panels, where NDT techniques (visual assessments, electrochemical and concrete soundness tests) have been conducted prior to destructive testing. Although visual inspection did not indicate poor concrete quality, the results of the ultrasonic pulse velocity testing showed that both concrete slabs are of poor quality and may be suffering from internal defects. Chlorides may have also been introduced through the strand conduit anchor points. These findings raise concerns regarding the structural integrity of corrosion-affected members.
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Analytical and experimental research was conducted to develop a design procedure for seismic retrofit of existing circular concrete columns using carbon fiber reinforced polymer (CFRP) jackets. The analytical research is an extension of earlier work on the development of a displacement based design procedure for column confinement. The experimental work involves full-size bridge columns tested under simulated seismic loading, consisting of constant axial compression and incrementally increasing lateral deformation reversals. The specimens are representatives of typical bridge columns between the footing and the point of inflection. One of the columns tested represents as-built conditions in practice with longitudinal reinforcement spliced near the base, providing an assessment of the deformability of existing columns. The test results indicate that the deformability of this column is limited to 1% lateral drift ratio. Companion columns with identical properties and CFRP jackets show that the deformability can be improved significantly through jacketing. CFRP jacketing of circular columns is effective in improving bond between reinforcement and concrete within the plastic hinge region while also confining the compression concrete. The lateral deformability of retrofitted columns shows improvements beyond 5% drift ratio. It is shown that columns satisfying the proposed design expressions develop ductile behavior, meeting the performance criterion adopted in design.
Experimental research was conducted to investigate the effectiveness of carbon fibre reinforced polymer (CFRP) jackets in retrofitting bridge columns with splice deficiencies. Full-size bridge columns were tested under simulated seismic loading. The columns were subjected to constant axial compression to simulate gravity loading, and incrementally increasing lateral deformation reversals to simulate seismic loading. The specimens represented typical bridge columns between the footing and the point of inflection. Tests of as-built columns were first conducted to assess their deformability in the inelastic range. The specimens included circular and square cross-sections with reinforcement arrangements that were representative of the majority of concrete columns in practice. The longitudinal reinforcement was spliced near the base. These columns had limited deformability and failed shortly after developing 1% lateral drift. Companion columns with identical properties were retrofitted with CFRP jackets and tested to investigate the effectiveness of the retrofit technique. The results indicated that CFRP jacketing was effective in circular columns in improving bond between reinforcement and concrete within the plastic hinge region. The lateral deformability of the circular column improved beyond 6% drift ratio. The CFRP jacket however was not as effective in the square column. The improvement observed in this column was limited to 2% lateral drift, beyond which there was a clear deterioration of the bond within the splice region, as evidenced by significant and rapid strength decay. For the covering abstract see ITRD E123557.
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(T 1 )), which is currently the most widely used intensity measure in probabilistic seismic demand analysis.
