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Simple relationships are proposed in this paper by modifying the Schmertmann et al. (1978) equation for foundation settlement estimations of sands both in saturated and unsaturated conditions. The modified method can be used for axi-symmetric footings (i.e., B/L ≈ 1) carrying vertical loads. This method is developed using the results of surface and embedded model footings tests (PLTs) and model cone penetration tests (CPTs) conducted in a controlled laboratory environment. The developed method is validated using in-situ data obtained from six large-scale footings and CPTs tested in unsaturated sands. The results of the study are encouraging to the practicing engineers as they are simple and provide reliable estimations of the settlement of shallow footings in both saturated and unsaturated sands from CPTs results.
Research has shown that the addition of steel fibers to concrete results in improved postcracking tensile capacity leading to enhanced toughness, ductility, and damage tolerance. These performance enhancements make steel fiber-reinforced concrete (SFRC) an ideal material for use in the blast-resistant design of structures. Research in the literature is conflicting on the performance of SFRC at high strain rates. There is also very limited research on the performance of SFRC structural components under blast loads. This paper presents the results of a research program investigating the blast performance of reinforced concrete and steel fiber-reinforced concrete columns. In the experimental program half-scale columns were constructed and exposed to different simulated blast pressure–impulse combinations using the state-of-the art shock-tube testing facility at the University of Ottawa. The test parameters included transverse reinforcement spacing (nonseismic and seismic detailing) as well as steel fiber content (0 to 1.5% by volume of concrete). The results show that SFRC improves the blast performance of columns in terms of maximum and residual displacements as well as damage tolerance and elimination of secondary blast fragments. Furthermore, the results demonstrate that the use of seismic detailing improves blast performance. Finally, the paper examines the suitability of using single-degree-of-freedom (SDOF) analysis to predict the blast response of the SFRC columns tested in the research program.
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For the past few decades, there has been an increase in awareness regarding the safety of highway bridges from blast loads. Since abutments/Retaining walls (RWs) are portions of bridges, investigating abutments/RW or RW behaviour under blast loads is important. As there have not been any studies investigating the dynamic response of retaining walls due to blast loading, an experimental study was conducted to examine the influence of blast loads on the dynamic behaviour of reinforced concrete retaining wall (RCRW) with sand as a backfill material. A shock tube was used to generate blast loads on the soil-RW model. The influence of the relative density, backfill saturation, blast load intensity, and traffic load equivalent surcharge on the blast behaviour of RCRW with sand backfill was studied. The results showed that the modes of wall movement were affected by the backfill relative density, blast load intensities, and degree of saturation. Under the same load conditions, an increase in the wall movement was noticed in loose backfill, and a translation response mode was evident in this condition. A relationship between wall relative movements and mobilized earth pressure coefficients was determined. The mobilized passive resistance of the RW backfill induced by blast load was used to determine the force–displacement relationship. Acceleration time histories for RW/backfill were found for all conditions. The findings of this research will help to properly evaluate and design bridges’ abutment and to develop resilient transportation infrastructure systems.
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Modeling the expansion and damage generated by alkali-silica reaction (ASR) in reinforced concrete structures is quite complex, yet necessary to obtain accurate predictions of the structural responses of distressed concrete members. Several ASR models have been developed over the past decades to predict expansion and damage at the material (microscopic) or the structural (macroscopic) scales. However, those models tend to either neglect or overemphasize the critical physicochemical parameters of the reaction, which limits their applicability. Therefore, a new simple yet reliable finite element approach is proposed in order to fill this gap. It accounts for the most important parameters affecting ASR through an engineering approach, without the need for non-technical guesses or to “fit” model parameters. The proposed model is validated through the computational simulation of reinforced concrete specimens cast and monitored in the laboratory. An application example of a real ASR-affected bridge is also provided.
This paper presents performance of steel buildings and nonstructural elements during the 27 February 2010 Maule Earthquake in Chile. Structural steel buildings are not common in Chile, due to the relatively high cost of material. The majority of damage to steel structures was observed in industrial facilities. In general, the structural steel buildings performed well. Limited damage was observed in some of the older buildings. Extensive damage was sustained by nonstructural elements, including masonry infill walls, suspended ceilings, partition walls, and architectural features. Brick masonry partition walls, commonly used in Chilean buildings, suffered damage when used in frame buildings with little drift control. The paper presents a summary of observed damage and a comparison of Chilean and Canadian design practices for steel buildings, with lessons drawn from observed structural performance.
A simplified nonlinear sectional analysis approach (NLSA) of aged reinforced concrete beam-columns based on numerical integration, enhanced inspection, material testing and/or empirical estimation of materials deterioration due to reinforcement corrosion is proposed. The proposed procedure is an iterative nonlinear technique that uses numerical integration of the sectional stresses and satisfies force equilibrium in every load increment step. The NLSA model incorporates corrosion-induced damage by reducing the steel cross section and ductility, removing the loss of concrete cover, and accounting for the loss of local bond in corrosion-damaged zones. Two case studies are presented to estimate the effects of corrosion on the structural behaviour of reinforced concrete beam-columns by taking into account critical damage states. The model results show good agreement with test results, high numerical stability and consistent convergence for all examined loading cases.
The experimental behavior of lap-spliced reinforced concrete beams subjected to high strain rates on the order of 1.0 s−1 was studied. Eleven companion pairs of beams, each consisting of two nominally identical specimens, were designed, built, and tested under low and high strain rates. The physical and material properties of the companion pairs were selected based on a range of design parameters known to significantly influence bond strength (i.e., the size of the spliced reinforcement, cover depth, concrete strength, and presence of transverse reinforcement). Results of the experiments demonstrated that although the underlying flexural response and nature of bond splitting failure was not affected by dynamic loads, the strength and stiffness of reinforced concrete beams was significantly improved when subjected to blast loading. Part of this increase was attributed to improvements in the load carrying capacity of the lap splices due to high strain rate effects. An average dynamic increase factor (DIF) applied to a bond of 1.28 was measured. Regardless of the strain rate, it was found that the bond strength of splices with and without transverse reinforcement increased in proportion to the ratios of the minimum cover depth and the splice length to bar diameter, respectively.
