摘要:

Recent earthquakes around the world have confirmed the poor seismic behavior of reinforced concrete bridge piers incorporating typical pre-1971 reinforcement details. Since the 1971 San Fernando earthquake in California, procedures to evaluate accurately the flexural and shear behavior of reinforced concrete bridge piers, as well as retrofit techniques to address economically the most common deficiencies, have been elaborated. In eastern Canada, the majority of reinforced concrete bridge structures incorporate piers with similar reinforcement details as those that suffered severe damage, or collapse, during recent earthquakes in California and Japan. Very little research, however, has been conducted on the seismic behavior of these structures, which often exhibit complex cross-sectional geometries and lap-splices in the plastic hinge region. This paper presents a contribution towards a better understanding of the seismic behavior and retrofit of reinforced concrete bridge piers in eastern Canada through quasi-static tests performed on five 1/3.65-scale pier models of an existing bridge structure in the Montreal region. The first specimen was tested in its existing conditions, while the four others were retrofitted with steel jackets. The geometry of the jacket, the size of the gap at the base of the pier, and the properties of the fill material between the jacket and the original cross section were investigated in these last four tests. A numerical model, considering the bond-slip between the concrete and the longitudinal reinforcement, is proposed to simulate the experimental results.Key words: bond-slip, bridge piers, ductility, hysteresis loops, lap-splices, seismic retrofit, steel jackets.

ISSN:0315-1468    

DOI:10.1139/l99-029

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents a more realistic and comprehensive static analysis technique for structures having non-prismatic members. In the proposed method a general stiffness matrix for non-prismatic members that is applicable to Timoshenko beam theory has been derived. The stiffness coefficients have been determined for constant, linear, and parabolic height variations of members, employing analytical and (or) numerical integration techniques. Uniform, triangular, and trapezoidal distributed loads over the entire member or along any part of it, concentrated loads, moments at points on the member, and any of these load combinations are taken into consideration to determine the fixed-end forces. A computer program has been coded in Fortran which analyses two-dimensional frames using the proposed stiffness matrix and fixed-end forces for a wide range of external loads. The fixed-end forces may include the effect of shear deformations. The importance of the shear deformations in non-prismatic members with high depth-to-span ratios is shown using numerical examples. The accuracy of the proposed analysis technique is verified by comparing the results of the numerical examples with those obtained from the general analysis program SAP90 using a large number of subelements.Key words: computer programs, fixed-end forces, loads (forces), non-prismatic (tapered), shear deformations, stiffness, structural analysis.

ISSN:0315-1468    

DOI:10.1139/l99-037

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Thousands of bridges throughout the United States have been identified as being scour critical (i.e., susceptible to failure from pier and (or) abutment scour). Scour occurs during times of rapid river flow when sediments, including rocks, gravel, and silt, are transported by the currents, undermining bridge pier foundations and similar structures. It can be increased by the presence of an ice cover. The scour process is dynamic; erosion and deposition can occur during the same high-energy river event, so the worst-case and the net effect cannot be easily predicted or dynamically monitored using previously available equipment. Herein, a technique and system (U.S. Patent #5,790,471) employing frequency modulated - continuous wave (FM-CW) reflectometry are discussed. This system is proposed for continuous monitoring of the extent of scour around riverine structures. A bench scale version of the system with a 490-MHz linearly swept bandwidth was implemented and tested in the laboratory, where sediments were incrementally added to a water-filled plastic barrel containing an 86-cm-long scour probe. Reflectometer data were taken after each increment of sediment was added. The data indicating the sediment boundary were plotted in a waterfall format that clearly shows the progressive sedimentation. This system has the potential for continuous round-the-clock operation and accuracy to within 5 cm of sediment depth.Key words: reflectometry, real-time monitoring, frequency modulated continuous wave, scour, sediment transport.

ISSN:0315-1468    

DOI:10.1139/l99-041

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A 12-month pilot plant study was conducted to evaluate a number of corrosion control treatments to reduce metal leaching from typical household plumbing materials. A pipe loop system was used to test six treatment options, with a control loop of the characteristically soft, acidic, Greater Vancouver Water District (GVWD) water. Four pH- alkalinity combinations and two concentrations of zinc orthophosphate (0.37 mg/L and 1.0 mg/L as Zn) were studied. at regular intervals, the flowing, treated, and control waters were allowed to stagnate in the pipe loop system for 8- and 16-h periods. Following the designated standing time, water samples taken from the lead/tin solder jointed, soft copper plumbing coils, the submerged, free standing coils of 50/50 lead/tin solder, and the brass faucets, were measured for lead, copper, and zinc levels. Overall, when compared to the control loop, the pH-alkalinity treatments appeared to exacerbate metal leaching in standing samples. The zinc orthophosphate treated loops were both effective at reducing lead and copper leaching to below control levels. In general, the two standing times showed little difference in the levels of leached metals. The exception to this occurred in the higher dose zinc orthophosphate loop, which had higher copper and zinc levels at the longer standing time.Key words: copper, corrosion, drinking water, lead, zinc orthophosphate.

ISSN:0315-1468    

DOI:10.1139/l99-047

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Seasonal variation of temperature and moisture causes considerable changes in the load-carrying capacity of pavements in geographical areas subjected to extreme freeze/thaw conditions. The Seasonal Monitoring Program (SMP) of the Long Term Pavement Performance (LTPP) study of the Federal Highway Administration (FHWA) monitors seasonal variations in Falling Weight Deflectometer (FWD) deflections, air temperature, rainfall, soil temperature, moisture content, and soil electrical resistance at numerous sites across North America. This study relates changes in pavement load carrying capacity represented by the pavement layer resilient moduli to selected environmental factors for a test pavement site in southwestern Manitoba. The significant environmental parameters causing seasonal variation in pavement layer resilient moduli are identified as the surface temperature for the asphalt layer and the thawing index for base and subgrade layers. The resilient moduli of various pavement layers show a substantial decrease in magnitude with increasing values of respective environmental parameter. The present model can be used for preliminary verification of empirical pavement design and rehabilitation practices currently in use to account for seasonal variations.Key words: asphalt, backcalculation, falling weight deflectometer, freezing, pavements, moisture, resilient moduli, seasonal variation, thawing, temperature.

ISSN:0315-1468    

DOI:10.1139/l99-049

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper describes the developments of operating rules for the Malahayu reservoir system in Indonesia. The analysis in this study is based on the use of a simulation model with a nested network flow optimization subprogram, which required hydrologic time series of reservoir inflows as input data. Since estimates of historic naturalized flows were of insufficient length, they were used as a basis for developing a 100-year stochastic series which offered a more challenging input while preserving the relevant statistics of the original historic series. This study shows by how much the reservoir yield could have been increased in the past, assuming that short-term inflow and demand forecasts are available and that the proposed reservoir operating rule is obeyed. The increase is estimated by comparing the long- term average of the simulated diversions at the three weirs with the actual historic diversions which are on the record. A more efficient reservoir operating policy would increase the reservoir yield by 38% in the March-June period and by 33% in the July-October period. If additional local runoff into the weirs is utilized in the same period, the increased supply would range up to 66% in the March-June period and 43% in the July-October period. The results from this study provide a strong argument in favour of investing in modern technology as opposed to massive additional infrastructure development.Key words: linear programming, reservoir rule curve, simulation, optimization, stochastic inflow series.

ISSN:0315-1468    

DOI:10.1139/l99-051

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Many sanitary and storm sewer networks are old and deteriorating rapidly. Water and sanitation managers are becoming more and more aware of the negative impact of poorly maintained sewer networks, especially since they are asked to comply with stricter environmental standards under already challenging budget constraints. The best way to improve the structural condition of a sewer network is to replace failed pipe sections. Planning replacement works necessitates knowledge of the present structural state of the network and of the evolution of this state in the near future. Towards this goal, a predictive modelling strategy was developed for the structural state of a sewer network. A case study in a Quebec municipality is presented to illustrate how the modelling strategy developed can be used to simulate the evolution, over the next 20 years, of the length of a sewer network in poor state, and to assess the impact of different replacement strategies on the global state of the network.Key words: urban infrastructures, sewers, structural state, modelling.

ISSN:0315-1468    

DOI:10.1139/l99-054

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

An interview survey of Alberta-based construction contractors was conducted in July and August 1998. The purpose of this survey was to elicit information on the factors that cause unanticipated project cost escalation during construction, from the contractor's perspective. This paper presents the findings of this survey and a proposed method of modeling the factors identified. The majority of factors identified impact labour productivity, which is a major source of cost overruns. A combination of subjective, objective, and secondary indicators are used to measure these factors and to assess their impact on project performance. The main conclusion of this survey is that many of the factors affecting the cost of construction are evaluated in subjective and imprecise terms and are difficult to quantify. This paper presents a method of modeling these factors using fuzzy membership functions, which capture the imprecision and subjectivity associated with the measurement of these factors. It discusses a basis for the definition of these membership functions and a method of calibrating these functions to make them more widely applicable to suit different contexts. These membership functions are being incorporated in a set of expert rules, which reason about the factors affecting costs, their impact on the project, and the appropriate corrective actions. These expert rules are being developed as part of a fuzzy expert system for construction project monitoring and control. A method of calibrating membership functions to suit individual contexts is currently being developed, which would be a significant advancement in the area of fuzzy logic.Key words: construction, costs, expert systems, fuzzy logic, project control, survey.

ISSN:0315-1468    

DOI:10.1139/l99-057

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Brittle punching failure of flat plates can occur as a result of transfer of shearing forces and unbalanced moments between slabs and columns. During an earthquake, the unbalanced moments transferred between slabs and columns can produce significant shear stresses that increase the likelihood of brittle failure. This brittle punching failure mode must be avoided for seismic-resistant flat plate structures. The most common punching strengthening methods are provision of the slab-column connections with drop panels or shear reinforcement or use of high strength concrete in the slab at the vicinity of the connections. This paper compares the effect of these punching strengthening methods on the ductility of slab-column connections. The results of a part of an extensive experimental program conducted on edge slab-column connections, without and with shear reinforcement, are presented. The experiments show that provision of stud shear reinforcement results in seismic-resistant slab-column connections, in which brittle punching failure is avoided in severe earthquakes. The connections with stud shear reinforcement can undergo ductile deformations associated with up to 5% lateral interstorey drift ratio, without loss of resistance to punching due to gravity loads.Key words: concrete design, ductility, energy dissipation, flat slabs, lateral drift, moment transfer, punching, seismic, shear strength, slab-column connections, stiffness, stud shear reinforcement.

ISSN:0315-1468    

DOI:10.1139/l99-052

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The use of clay and wood waste in construction materials points out to a sensitivity to water, which is susceptible to reduce their durability. This work has first been interested in the influence of different constituents on the extreme dimensional variations (EDV) of such cementing composites. A formulation allowing the conciliation of environmental imperatives, interesting mechanical and thermal characteristics, and low density has been proposed. However, the EDVs remain above the required objective. In order to reach this value, different treatments have been examined. The addition of alkali-resistant fiberglass in the matrix did not lead to satisfactory results. Not only is the reduction of the EDVs insufficient for reasonable proportions of fibers, but this treatment also increases the proportion of absorbed water in presence of liquid water. Taken separately, both types of treatments used for wood particles - neutralization with hydraulic binders and extraction with boiling water of hydro-soluble compounds - also do not allow a sufficient reduction of EDVs. However, the combination of these two treatments allows the achievement of EDV1 mm/m. Such a treatment improves the mechanical resistance without significantly altering the thermal performances.Key words: wood concrete, extreme dimensional variation, fiberglass, neutralization, hydrolysis.[Journal translation]

ISSN:0315-1468    

DOI:10.1139/l99-070

出版商:NRC Research Press    

年代:2000

数据来源: NRC