The Mission Bridge carries Highway 11 over the Fraser River between Mission and Abbotsford. It is a critical link in the Province’s disaster recovery network, connecting industry, residents, and medical facilities between these two communities. The crossing is one of the Lower Mainland’s major river and harbour crossings, for which the Province embarked on an ambitious seismic retrofit program, spurred in large part by the Loma Prieta earthquake in San Francisco in 1989 – 25 years ago this past October. This bridge is founded on deep, liquefiable sands over a major river, and has many of the seismically vulnerable details and features found in bridges constructed prior to the 1980’s. The bridge has been seismically retrofit and rehabilitated in several construction contracts performed over the past several years. Works completed through 2012 included structural seismic upgrades to provide enhanced deformation capacity, ground improvements such as compaction piles, stone columns, berms and other works, and superstructure rehabilitation and strengthening works. In 2012, the last seismic retrofit for the bridge was to densify the loose sands and silts at substantial depth to mitigate lateral spreading deformations of the south riverbank and the consequential damage to Pier S4. The propensity of the soils to spread laterally during seismic shaking, and the large (2.4 m) and very lightly reinforced rectangular concrete columns combined to create a significant seismic vulnerability and a high risk of damage or collapse from a moderate earthquake. A trial ground improvement contract near S4 was performed owing to the depth of soils being improved. The anticipated benefits to the soils for an economic layout and cost of compaction piles were not achieved, and alternative strategies were reassessed. The solution adopted was a combination of the geotechnical (ground improvement) benefits achieved by the trial compaction pile contract and column jacketing design to provide enhanced column deformation capacity. A new, innovative column jacket using ultra-high performance fibre-reinforced concrete (UHPFRC) was developed for the column ductility enhancement. The seismic behaviour of column jacket retrofits is well established, and use of UHPFRC to strengthen, improve spalling resistance, or improve durability of concrete piers is growing. However, to provide the necessary curvature ductility capacity to existing large rectangular columns, steel or concrete column jackets are typically stiff, large, expensive and visually obtrusive. The use of UHPFRC offered a solution to all of these concerns. This paper describes the options assessment and selection, the displacement-based seismic design approach, and the construction aspects of the ductility-enhancement retrofit for Pier S4 of this bridge. Materials use, quality assurance, and construction issues are discussed. This approach offers a new approach to retrofit that designers can consider for the retrofit of older, large rectangular concrete columns.

The De la Concorde Overpass in Laval, Quebec, Canada failed in 2006 and cost the lives of five people. The failure initiated in the half-joint of the thick cantilever slab that supported the drop-in span. Following this failure, a number of owners across Canada evaluated non-redundant half-joint connections of concrete bridges, including the Margaret Avenue Bridge in Kitchener, Ontario, Canada. This paper describes the evaluation of the half-joint detail of the structure including review of existing information and a discussion of uncertainties that led to the closure and demolition of the structure. The paper critically compares observations during the demolition of the structure with the assumptions made during the evaluation. The findings during demolition confirmed the majority of the assumptions and validated the decision to demolish the structure.

The impact response of reinforced and posttensioned concrete members with ultrahigh-performance fiber-reinforced concrete (UHPFRC) overlay was studied. This paper presents the results of nine drop weight slab strip tests. Major parameters for the tests were the reinforcement configuration of the concrete substrate, the addition of reinforcing bars in the UHPFRC layer, and the static system. Two reinforced and posttensioned concrete slabs were tested for reference. Five slab strips were tested under static loading conditions for comparison. A three-point bending and a cantilever system were used in the drop weight tests to induce flexural compression or tension in the upper UHPFRC layer. The addition of a UHPFRC overlay improved the structural response: no crushing or spalling occurred in the UHPFRC at the impact location. The UHPFRC had a load distributing function, which led to reduced crack widths in the substrate and lower member deflections.

The mix design of ultra-high performance fibre reinforced concretes (UHPFRC) produced with locally available materials in Quebec and Ontario is presented. The procedure and results of the optimization of self-consolidating UHPFRC are discussed. The characterization of the retained mixes is presented with regards to strength, heat of hydration, shrinkage, chloride ion permeability, and freeze–thaw resistance. The results show that it is possible to produce self-consolidating UHPFRC with the targeted properties for use in precast products and in situ applications without requiring heat or pressure treatment during curing.

This paper presents an experimental and analytical study of rate-dependent ultra-high performance fiber reinforced concrete (UHPFRC) behavior. UHPFRC three- and four-point bending response was determined on plates subjected to quasi-static loading. Drop weight tests were performed in order to apply dynamic three-point-bending loading to UHPFRC plates. In addition, uniaxial tensile tests were performed at different strain rates. A cross-sectional bending model related the uniaxial tensile behavior to the bending response with good agreement. The equivalent static response of the plate specimens in the drop weight tests was successfully determined with nonlinear mass–spring models. The results of this study show a significantly increased strength and fracture energy of the dynamically loaded plates when compared to quasi-static loading and confirm the validity of the analytical modeling.

Composite ultra-high-performance fiber-reinforced concrete (UHPFRC) and conventional reinforced concrete structural members are investigated to assess the rehabilitation potential for existing concrete structures. The composite structural response is determined by testing 12 full-sized flexural beams, loading the UHPFRC layer in tension. The results demonstrate that the exceptional material properties of UHPFRC significantly improve the composite member structural response; including the ultimate force, stiffness, and cracking behavior. An analytical model is developed to predict the composite UHPFRC and conventional reinforced concrete structural response, and is employed to further analyze the experimental test results.

Knowledge of the mechanical properties, i.e. strength, stiffness and deformation capacity, of cementitious materials at any arbitrary time is fundamental for operations such as removal of formwork, prestressing or cracking control. This paper presents a study of the evolution of indexes related to hydration and their correlation to the development of the mechanical properties for an Ultra-High Performance Fiber Reinforced Concrete (UHPFRC), The hydration kinetics was determined using semi-adiabatic heat of hydration tests, and the mechanical properties were investigated experimentally at several ages between 3 and 365 days and then described with models originally developed for conventional concretes. Models and experiments were in good agreement. Furthermore, it was observed that for the UHPFRC, the rate of development of mechanical properties was highest for the secant modulus, followed by the compressive and then the tensile strength. (C) 2006 Elsevier Ltd. All rights reserved.

Structural elements combining Ultra-High Performance Fiber Reinforced Concretes (UHPFRC) and concrete offer a high potential in view of rehabilitation and modification of existing structures. The investigation of the time-dependent behavior of composite “UHPFRC-concrete” elements is a fundamental step in the determination of durability and serviceability. For this, an experimental program was conducted on large composite “UHPFRC-concrete” beams and a numerical model was validated with the test results. The experimental results and a parametric study performed with the numerical model showed that UHPFRC and normal strength reinforced concrete are compatible in the long-term and that the critical period of composite “UHPFRC-concrete” elements are the first 90 days after the casting of the UHPFRC layer. Thus, the high potential of such composite elements can be exploited also in the long term.

This article describes a study of concrete members rehabilitated with an overlay of Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) that were subjected to high strain rates. UHPFRC is ideally suited for use in rehabilitation and strengthening of structures. The material has strength of 160 MPa in compression and 8 MPa in tension, and exhibits strainhardening behaviour under uniaxial tension. Its fracture energy (typically about 20 000 J/m) is 130 times greater than that of conventional concrete. In addition, its dense matrix leads to a very low permeability, thus preventing the ingress of detrimental substances and considerably extending durability. Existing concrete structures can be successfully rehabilitated by adding UHPFRC overlays. The objective of this study was to investigate the structural performance of such composite “UHPFRC-concrete” members subjected to impact loading. Typical load cases inducing high strain rates are vehicle impact, explosion or rockfall. UHPFRC plates were impacted with a drop-weight in bending in order to determine their impact resistance. Static bending tests were also performed on specimens for comparison. Finally, ongoing static and drop-weight tests on slab strips consisting of UHPFRC and normal strength reinforced concrete are briefly described.

The use of ultrahigh-performance fiber-reinforced concretes (UHPFRC) improves the structural response and extends the durability of concrete structures. Three basic configurations for structural elements combining UHPFRC and reinforced normal strength concrete are proposed with regard to typical demands on rehabilitation projects. They fulfill a protection function and the resistance can be increased if required. The flexural response of these composite UHPFRC–concrete elements is investigated with an original analytical cross-sectional model in a parametric study: UHPFRC increase stiffness and resistance and delay the formation of localized cracks. For this, a minimum magnitude of strain-hardening of 0.2% is necessary. Additional reinforcement in the UHPFRC layer is the most efficient way to increase the bending resistance. The investigation demonstrates how to use UHPFRC and reinforcing bars best in rehabilitation of existing concrete structures.

Ultrahochleistungsfaehige Faserbetone (UHPFRC) bieten sich aufgrund ihrer hervorragenden Werkstoffeigenschaften fuer die Instandsetzung und Veraenderung bestehender Betonbauten an. Experimentelle, numerische und analytische Untersuchungen zeigen, dass der Tragwiderstand und die Steifigkeit in UHPFRC-Beton-Bauteilen erhoeht sind und dass sich infolge interner Verformungen und unter Gebrauchslasten keine lokalisierten Risse bilden, was zu einer deutlichen Verlaengerung der Dauerhaftigkeit fuehrt. Mit schlaffer Bewehrung in der UHPFRC-Schicht kann der Tragwiderstand deutlich erhoeht und die Bildung lokalisierter Risse verzoegert werden. Die Tragwerksantwort unter Biegung kann mit einem analytischen Querschnittmodell ermittelt werden. Drei Grundkonfigurationen fuer UHPFRC-Beton-Bauteile werden fuer die Anwendung bei Instandsetzungsprojekten vorgeschlagen. (A) ABSTRACT IN ENGLISH: Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) are ideal materials for rehabilitation and modification of existing concrete structures due to their outstanding material properties. Experimental, analytical and numerical studies show that resistance and stiffness are significantly improved in composite UHPFRC-concrete elements. No localized cracks are formed due to internal UHPFRC deformations and under service conditions leading to a significant extension of durability. Reinforcement bars in the UHPFRC layer increase significantly the resistance and delay the formation of localized cracks. The structural response under bending can be determined with an analytical cross-sectional model. Three typical configurations are proposed for composite UHPFRC-concrete elements for rehabilitation projects. (A)

Structural Elements combining Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) and Concrete: An innovative solution for rehabilitation and modification of existing concrete structures Ultra-High Performance Fibre Reinforced Concretes (UHPFRC) are ideal materials for rehabilitation and modification of existing concrete structures due to their outstanding material properties. Experimental, analytical and numerical studies show that resistance and stiffness are significantly improved in composite “UHPFRC-concrete” elements. No localized cracks are formed due to internal UHPFRC deformations and under service conditions leading to a significant extension of durability. Reinforcement bars in the UHPFRC layer increase significantly the resistance and delay the formation of localized cracks. The structural response under bending can be determined with an analytical cross-sectional model. Three typical configurations are proposed for composite “UHPFRC-concrete” elements for rehabilitation projects.

Note: edited by Swedish Cement and concrete Research Institute (CBI) RILEM PRO 43 : International RILEM TC 193-RLS Workshop on Bonded Concrete Overlays Reference MCS-PRESENTATION-2007-014 URL: http://www.rilem.net/ Record created on 2007-05-23, modified on 2016-08-08

Rehabilitation projects aim to enhance durability and to ensure structural safety. Ultra-High Per-formance Fibre Reinforced Concretes (UHPFRC) may fulfil these requirements when used as conservation materials. The structural response of composite “UHPFRC-concrete” elements under 4- point-bending was studied by means of experiments and an analytical model with the UHPFRC layer being under tension. Different depths of the UHPFRC layer were tested and rebars were placed in the UHPFRC layer in order to enhance the structural response. The re-sults demonstrate the outstanding mechanical properties of UHPFRC in terms of structural re-sponse in composite elements. The addition of rebars in the UHPFRC layer enhances significantly resistance and stiffness and delays crack formation. An original analytical model allows to predict the moment- curvature relationship of composite “UHPFRC-concrete” elements.

Reference MCS-CONF-2007-035 URL: http://www.sc.kutc.kansai-u.ac.jp/conference/IABMAS2004/ Record created on 2007-05-23, modified on 2016-08-08

Note: Eds. G.L. Balasz & Borosnyoi Reference MCS-CONF-2007-030 Record created on 2007-05-08, modified on 2016-08-08