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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.
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<p>The impact of climate change on key environmental variables is well-known; yet its effect on complex phenomena such as corrosion due to carbonation and chloride ingress remains a subject of ongoing debate. This study reviews key experimental and modeling research addressing the combined effects of carbonation and chloride penetration in concrete structures. While studied individually, their combined effect remains less understood. Chloride ion ingress is particularly relevant in marine environments, where salt spray and carbonation may occur concurrently. Similarly, structures in urban areas exposed to de-icing salts and high</p><p>&#119862;&#119874;2 levels due to traffic and pollution face increased corrosion risks. Previous research suggests that carbonation can significantly influence chloride ion transport in concrete, but its exact effect, whether it accelerates or decelerates damage, varies across studies. Understanding this interaction is crucial for improving durability predictions and developing effective mitigation strategies.</p>
Flexural beam-end tests were conducted to characterize the effect of high strain rates on reinforcement bond in concrete. A total of 14 flexural beam-end bond specimens, constructed with 20 M deformed reinforcement embedded in 50 MPa concrete, were tested. The beam-ends were subjected to static and dynamic testing generating strain rates of 5.0 × 10−6 s−1 and 1.2 s−1, respectively. Half of the beam-ends were constructed with lengths of bonded reinforcement of 200 mm, with the remainder having a longer bond length of 400 mm. The bond stress-slip response of the specimens was constructed using elastic strain measurements obtained from the bonded region. High strain rates were found to significantly enhance the bond strength of the beam-ends, whereas they did not significantly influence the general shape of the bond stress-slip curves. Bond strength obtained under rapid loading conditions exhibited approximately the same strain rate sensitivity as has been observed by others in the literature for similar high strain rate tests. Flexural beam-end tests were found to be well suited for high strain rate testing, and are recommended for future studies, provided a safe and convenient dynamic loading fixture can be employed.
With the advent of advanced materials and technology, construction materials are becoming superior in terms of not only strength but also durability. In recent years, the importance and necessity of using high-strength materials are recognized in many large-scale projects. Practicing engineers and researchers are also showing immediate interest in high-strength concrete (HSC) and high-strength reinforcement (HSR). The application of high-strength materials in construction combines the advantages of reducing the amount of materials, cross-sectional sizes, and reinforcement congestion. Although the application of HSC has been gaining popularity in high-rise building construction, parameters affecting the performance of reinforced concrete members made from high-strength materials are still under investigation. Besides, many construction material suppliers are promoting HSC and HSR to be used in construction due to their availability.
One of the applications of fiber-reinforced polymers in bridge construction is stay-in-place formwork. Fiber-reinforced polymer stay-in-place formwork, in the form of preformed tubes, provides easy form assembly, protection of steel reinforcement and concrete against corrosion and chemical attacks while also improving the strength and ductility of structural elements in earthquake resistant construction. Experimental research was conducted to investigate the seismic performance of fiber-reinforced polymer stay-in-place formwork for bridge columns. Tests of large-scale specimens were conducted under simulated seismic loading. The experimental program included circular and square columns confined with carbon fiber–reinforced polymer tubes. The results indicate that the use of carbon fiber–reinforced polymer tubes increases column inelastic deformability significantly. Bridge columns under low levels of axial compression exhibit inelastic drift capacities in excess of 4% before failing in flexural tension due to the rupturing of longitudinal reinforcement. These observations and experimental results were used to develop a displacement-based design procedure for concrete confinement for fiber-reinforced polymer–encased concrete columns. This article presents an overview of the experimental program and the design approach developed.
Modelling techniques for dynamic inelastic response analysis of coupled wall structures are investigated. Emphasis is placed on effects of parameters defining the force‐displacement hysteresis loop. Specifically, effects of axial force‐moment interaction, strength reduction, shear yielding, pinching, reloading and unloading branches of hysteresis loops are considered. Effects of modelling parameters on selected response quantities are investigated and discussed in detail. A 20‐storey coupled wall structure was selected for dynamic analysis. Ranges of parameters characterizing force‐displacement hysteresis loops were obtained from laboratory tests under slowly reversed static loading. Previously recorded strong motion accelerograms were used as input motions. Results indicate that wall axial forces and beam strength reduction can have significant effects on response envelopes. Moderate variations in unloading and reloading branches of hysteresis loops and pinching appear to have little effect on dynamic response.
An experimental investigation was conducted to assess the performance of a new buckling-restrained brace (BRB) system for retrofitting seismically deficient reinforced concrete frames. The BRB consists of a ductile inner steel core bar designed to yield in tension and compression without buckling while controlling the response to seismic forces. The core bar is contained within a tubular steel section, which in turn is housed in a larger tubular steel section infilled with mortar, providing lateral restraint against buckling. Self-consolidating mortar is used as filler material between the two tubular sections to increase the buckling resistance. The inner core bar is connected to innovative end units that allow extension and contraction during tension-compression cycles while providing lateral restraint against buckling. The new BRB system has been verified experimentally using two large-scale reinforced concrete frames, one of which was tested as a reference nonretrofitted frame and then repaired and retested three more times after BRB retrofits, while the other was retrofitted and tested, forming the fourth retrofitted frame test. Tests demonstrated substantial increases in the lateral load and energy dissipation capacities of retrofitted frames with satisfactory drift control. Three different types of steel bars with different strength and elongation characteristics were considered. Among the three, stainless steel provided the best strength, stiffness, and ductility enhancements.
Large‐scale reinforced concrete columns were tested to investigate hysteretic behavior of anchorage slip in reinforced concrete structures. The columns were subjected to constant axial compression and unidirectional and bidirectional lateral‐deformation reversals. The results indicate a significant increase in column rotation due to anchorage slip. Penetration of yielding into the column footing was observed in the tension reinforcement, while the compression yielding was localized at the column‐footing interface. Axial compression resulted in early closure of the crack associated with anchorage slip, reducing related deformations. An analytical model was developed for hysteretic moment‐anchorage slip‐rotation relationship. The model consists of a primary curve and a set of rules defining unloading and reloading branches. The primary curve is constructed by computing the extension and slippage of tension reinforcement in the adjoining member. This is accomplished by considering inelastic strain distribution along the embedment length of reinforcement, as well as the local bond‐slip relationship. Hysteretic rules are obtained from experimental observations, and incorporate pinching of hysteresis loops as well as the effect of axial compression. Comparisons of experimental and analytical hysteretic relationships indicate excellent agreement.
Four concrete block masonry and two reinforced concrete walls were designed to simulate low-rise nonductile walls built decades ago, before the enactment of earthquake-resistant design provisions. Two masonry walls were unreinforced and two were partially reinforced. The concrete walls had minimum reinforcement. One wall from each pair was retrofitted using a steel strip system consisting of diagonal and vertical strips that were attached using through-thickness bolts. Stiff steel angles and anchor bolts were used to connect the steel strips to the foundation and the top loading beam. All walls were tested under combined constant gravity load and incrementally increasing in-plane lateral deformation reversals. The lightly reinforced concrete walls were also repaired using only vertical strips and retested. These tests showed that the complete steel-strip system was effective in significantly increasing the in-plane strength and ductility of low-rise unreinforced and partially reinforced masonry walls, and lightly reinforced concrete walls.
