252 publications from this institution
An analytical procedure is proposed for the force‐deformation relationship of a reinforcing bar anchored in concrete. The procedure leads to computation of deformations in two parts, as extension and slippage. The extension of reinforcement is determined by establishing inelastic strain distribution along the embedment length of the bar. Constant average bond along the elastic length and frictional bond over the plastic length are assumed. The rigid body slippage of the bar is computed when the bar is stressed to the far end. An increase in the elastic bond stress is considered to develop the bar force with the available anchorage length. The elastic bond at the far end of the bar is used with a previously derived local bond‐slip model to obtain the rigid body slippage of the bar. The procedure is applied to straight as well as hooked bars, subjected to pull, and simultaneous push and pull, simulating exterior and interior joints. The results are verified against a large volume of experimental data reported in the literature.
This paper describes damage to bridges caused by the 1994 earthquake at Northridge, California. A description of the damage and the probable causes are presented for the seven bridges that suffered some form of collapse. The majority of damage was due to column shear or combined shear and flexure failures, but restrainer failure was the cause of collapse in one bridge. The lack of damage to other bridges and to foundations is discussed. Key words: Northridge, earthquake, seismic, bridges, damage, performance.
Two discussions of a paper with the aforementioned title by J. Hoshikuma, K. Kawashima, K. Nagaya, and A.W. Taylor, published in this journal (Volume 123, Number 5, May 1997), are presented. The first discusser presents a model that he proposed in 1991, which was developed on the basis of a large database including 63 column specimens with rectangular hoops from five different experimental programs. He also proposes that the effect of hook shape, the relationship between the strength of the unconfined specimens the authors tested to the cylinder strength, and the possible effect of longitudinal reinforcement warrant further investigation. The last two discussers present eight points that they believe deserve further attention before the authors' approach for confined concrete columns can be utilized. Discussions are followed by closure from the authors.
Observations on damage to concrete structures, due to the 1994 Northridge earthquake, are reported from a Canadian code perspective. Most of the damaged structures were older, nonductile, structures that do not conform to current design and detailing requirements. Concern is expressed about the seismic hazard of older Canadian structures having similar deficiencies. A significant number of parking structures suffered extensive damage and a number of precast concrete parking structures collapsed. Deficiencies in these structures include lack of proper diaphragm connections, a mix of gravity load columns with ductile framing, inappropriate number and distribution of shear walls, torsional effects caused by ramps, and the creation of short columns due to geometric features. This earthquake also demonstrated the deficiencies in connections of pre-1973 tilt-up structures. Key words: seismic design, earthquake, Northridge, structures, codes, concrete, precast concrete.
The performance of bridges during past earthquakes has clearly indicated that many structural failures could be attributed to inadequate seismic design of existing bridge structures. This paper reports on experimental research conducted to investigate the effectiveness of carbon fiber reinforced polymer (CFRP) jackets in retrofitting bridge columns with splice deficiencies. The test procedure is explained, and the test results, along with conclusions drawn from them are presented.
This paper discusses the behaviour of the rheological behaviour of corrosion products (produced in the laboratory) in a high alkaline environment to understand hydraulic-induced fracture by corrosion products in reinforced concrete. A mixture of iron powder, sodium chloride, calcium hydroxide, and water was used to produce corrosion products. The development of corrosion products was studied at 2, 4, 6, and 8-week intervals. Imaging techniques, along with rheological characterization methods, were conducted to understand the viscoelastic flow behaviour of corrosion products. The results show that corrosion products exhibited different rheologic properties throughout the corrosion process. Three iron oxide phases (Magnetite, Goethite, and Lepidocrocite) were detected throughout the initiation and propagation stages of corrosion in the laboratory. The corrosion products obtained for each study period behaved as colloidal materials, demonstrating all the characteristics of shear-thinning materials. As a result of chemical and particle disintegration, the viscosity of corrosion products decreased with the applied shear rate. In addition, the experimental data showed that the density and particle size of corrosion products decreased with time. These results can be used to understand the progress of corrosion's damage in reinforced concrete.
This paper consists of reported information divided into two general categories, performance of High-Strength Concrete (HSC) columns under concentric loads, and combined axial and bending moments. Presented is a brief summary of the highlights of the reported data.
No abstract is provided for this article.
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.
Lateral prestressing of concrete columns was investigated as a method of seismic retrofit. Experimental research was conducted to develop a design procedure for shear deficient concrete columns. The technology consists of external prestressing of columns in transverse direction by means of individual hoops that consist of prestressing strands and specially designed anchors. Seven full-scale columns were tested under constant axial compression and incrementally increasing lateral deformation reversals. The results, presented and discussed in this paper, indicate that the retrofit methodology can suppress shear failure, promote flexural behavior, and increase inelastic column deformability substantially. A design procedure is presented for seismic retrofit of shear-deficient columns to achieve two different levels of performance.
A parametric investigation was conducted to determine the significance of selected structural and ground motion parameters on dynamic inelastic response of coupled wall structures. Structural parameters include: fundamental period, wall strength, beam‐to‐wall stiffness and strength ratios, coupling arm, clear beam span, gravity loads, and structure mass. Ground motion parameters include: earthquake frequency characteristics, duration, and intensity. A computer program and a moment‐rotation hysteretic model, including the effects of axial force‐flexure interaction, was used to conduct nonlinear dynamic analyses. Significance of each parameter on maximum force and ductility response is shown. The most significant parameters are identified as design variables. Relationships between design variables and response quantities are established.
An experimental investigation was carried out to evaluate the post-blast capacity of CFRP protected reinforced concrete (RC) columns. A total of five half-scale RC columns were tested under simulated blast pressures using a shock tube testing apparatus. Three columns were strengthened with CFRP laminates of two different lay-ups, while the other two columns were left unprotected to serve as control columns. Results of this study proved that CFRP protected RC columns have substantially higher blast resistant and post-blast axial capacity than as-built columns. CFRP protection laminates containing ±45° woven laminas showed the best performance with the most ductile response.
Abstract Corrosion of reinforcing steel in reinforced concrete (RC) infrastructure is one of the most detrimental deterioration mechanisms, affecting both safety and serviceability. In the present study, a comprehensive analysis methodology of corrosion damage is adopted. The detrimental effects of corrosion‐induced degradation of material properties on the ultimate capacity of an existing aging RC bridge pier under concentric loading are investigated. A three‐dimensional nonlinear finite element analysis using the commercially available finite element program DIANA is used. The main corrosion‐induced deteriorating factors considered in the present study are: concrete strength degradation within the cover and part of the confined concrete core due to corrosion‐induced cracking, degradation of confinement effects, steel area reduction due to uniform corrosion (in both longitudinal and tie reinforcement), steel ductility degradation due to pitting corrosion, buckling of compressive steel bars due to cross‐section reduction and confinement degradation, and bond strength degradation between steel and concrete induced by concrete cracking/spalling. The methodology is evaluated by comparing the numerical results to those of corroded column tests reported in the literature.
Simple relationships are proposed in this paper by modifying the Schmertmann's equation for settlement estimations of footings (i.e., <TEX>$B/L{\approx}1$</TEX>) carrying vertical loads in saturated and unsaturated sandy soils. The modified method is developed using model plate load tests (PLTs) and cone penetration tests (CPTs) results conducted in saturated and unsaturated sand in a controlled laboratory environment. Seven in-situ large-scale footings tested under both saturated and unsaturated conditions in sands were used to validate the proposed technique. The results of the study are encouraging as they provide reliable estimates of the settlement of shallow footings in both saturated and unsaturated sands using the conventional CPT results.
Bridges are essential lifeline infrastructures that must remain in service after strong seismic events. Recent design codes implement performance-based design methodologies which may call for increased seismic demands. However, most of the existing infrastructure in Canada was built prior to the enactment of modern seismic codes of the post-1980 era. Recent earthquakes revealed seismic vulnerability of bridge structures with a number of deficiencies in regards to low seismic design force levels, inadequate column confinement and lack of column shear capacity. The objective of this study is to assess the vulnerability of reinforced concrete bridge columns in Canada. Computer software DRAIN-RC, developed for nonlinear dynamic analysis of reinforced concrete structures, was used to determine the deformation demands of bridge columns under selected Eastern and Western Canadian ground motions. Deformation demands were subsequently compared with available research data in the literature on column deformation capacities to assess seismic vulnerabilities. Results exhibit different levels of performance for existing bridge columns in different regions of Canada, with bridges in western Canada showing higher vulnerabilities.
Various numerical models have been developed to appraise alkali-silica reaction (ASR) induced expansion and to predict its potential to generate further damage. A previous work proposed a finite element approach that does not oversimplify nor overcomplicate the reaction analysis, while still being capable of representing the anisotropic expansion and its macroscopic consequences. Slender structures have already been successfully simulated using this approach, although it has never been applied to assess massive structures. This paper presents the validation analyses and the simulations performed on an ASR-affected dam in Brazil to appraise the accuracy of the previously proposed approach for massive structures. The results suggest that the numerical model is quite promising for appraising ASR development over time, based on the damage observed both in the field and on test specimens. Moreover, phenomena not directly accounted for in the model (such as alkali release from aggregates and the absence of an important amount of leaching) were found to play an important role in ASR-affected massive structures.
