Elin Jensen

Life-Cycle Cost Analysis of Alternative Reinforcement Materials for Bridge Superstructures Considering Cost and Maintenance Uncertainties

A life-cycle cost analysis (LCCA) was conducted on prestressed concrete bridge superstructures using carbon fiber reinforced polymer (CFRP) bars and strands. Traditional reinforcement materials of uncoated steel with cathodic protection and epoxy-coated steel were also considered for comparison. A series of deterministic LCCAs were first conducted to identify a range of expected cost outcomes for different bridge spans and traffic volumes. Then, a probabilistic LCCA was conducted on selected structures that included activity timing and cost random variables. It was found that although more expensive initially, the use of CFRP reinforcement has the potential to achieve significant reductions in life-cycle cost, having a 95% probability to be the least expensive alternative beginning at year 23–77 after initial construction, depending on the bridge case considered. In terms of life-cycle cost, the most effective use of CFRP reinforcement was found to be for an AASHTO beam bridge in a high traffic volume area.

Reliability Analysis of RC Beams Exposed to Fire

AbstractA procedure for conducting reliability analysis of RC beams subjected to a fire load is presented. This involves identifying relevant load combinations, specifying critical load and resistance random variables, and establishing a high-temperature performance model for beam capacity. Based on the procedure, an initial reliability analysis is conducted using currently available data. Significant load random variables are taken to be dead load, sustained live load, and fire temperature. Resistance is in terms of moment capacity, with random variables taken as steel yield strength, concrete compressive strength, placement of reinforcement, beam width, and thermal diffusivity. A semiempirical model is used to estimate beam moment capacity as a function of fire exposure time, which is calibrated to experimental data available in the literature. The effect of various beam parameters was considered, including cover, beam width, aggregate type, compressive strength, dead to live load ratio, reinforcement r...

Transport properties of concrete pavements with excellent long-term in-service performance

Abstract Excellent long-term performance in concrete pavements is associated with both concrete strength and durability properties like permeability and chloride ion penetration resistance. Water and air permeability are investigated, as is the rapid chloride permeability test (RCPT). Strong relations between compressive strength and permeability and chloride ion penetration resistance of typical ordinary Portland cement (OPC) concrete pavements are observed. Effects of environmental exposure on permeability and RCPT results are explained. Through-depth variation of permeability and RCPT results within a pavement slab are shown and discussed.

Validating Top-Down Premature Transverse Slab Cracking in Jointed Plain Concrete Pavement.

Built-in negative temperature gradients from hot weather construction have the effect of shifting the entire temperature gradient distribution such that the slab is predominantly upward curled. This condition in turn greatly increases loss of slab support, which was the major factor promoting premature top-down midslab transverse cracking for a jointed plain concrete pavement (JPCP) Interstate project in southeastern Michigan. Finite element analysis predicts that loss of slab support, maximum at the joints, shifts the maximum stress during truck loading at the joints toward midslab in JPCP, coinciding with maximum curling stresses. A built-in upward-curled slab condition was quantified from joint corner deflections and slab temperature measurements. Slab surface elevation profiling using the dipstick device verifies that these slabs are permanently upward curled and that loss of joint support is a function of daily changes in slab surface temperature. Detailed falling-weight deflectometer slab deflection profiles show that loss of slab support along the outer edge for this project exceeds 800 microns at the joint during morning temperature conditions typical for summer and fall in Michigan, corresponding to a nearly fivefold increase in outer edge joint deflection as measured during the afternoon, during which time the slab is in full contact with the base. The loss of slab support extends inward toward the slab middle, creating a “rocking chair” condition typical for short slab behavior, which allows the slab to rock if loaded only at one joint. This condition is underscored by field observations. During morning and evening testing, when the pavement surface was cooler, there was a noticeable rocking sensation at the joints when loaded trucks passed in the adjacent lane. Later in the afternoon, after the pavement temperature rose, the movement stopped.

CRACK RESISTANCE OF JOINTED PLAIN CONCRETE PAVEMENTS

The crack sensitivity of jointed plain concrete pavement is investigated experimentally in the laboratory for a limited number (seven) of large-scale slabs and numerically as well using nonlinear fracture mechanics. The basis for modeling is the concrete crack-width relation and the elastic modulus. The stress-crack width relations for the concrete were obtained on the concretes tested in the laboratory. The slab dimensions in the experimental and numerical analysis were 1.8 m wide and 3.0 m long, and a full-depth cross section (250 mm) containing a full-width surface crack extending 20% to 25% of the slab thickness was used. The major findings are that the numerical analysis verifies that the results from laboratory testing resemble field fracture behavior. Further, irrespective of the aggregates used, a concrete pavement is highly crack sensitive, although the coarse aggregate can affect the sensitivity by approximately 30%. The experimental and numerical results showed that a crack-to-slab-thickness ratio of 20% to 25% reduced the in-plane tensile capacity of the cracked section by 60% to 75% depending on the concrete used.

Fracture Energy Test for Highway Concrete: Determining the Effect of Coarse Aggregate on Crack Propagation Resistance

Portland cement concrete fracture properties—specific fracture energy, fracture toughness, and brittleness—were investigated for typical Michigan highway concretes containing different coarse aggregates and varying in age: 7,28, and 91 days. These fracture properties can be determined from the complete load-deflection curve of a notched beam. The effective beam is 965 mm long, 100 mm wide, and 200 mm high, with a 100-mm center notch. Results show that the specific fracture energy, which determines the resistance to crack propagation, for a concrete pavement mix is controlled primarily by the coarse aggregate type. Differences of 100 percent were obtained between aggregate types. A glacial gravel yielded the highest resistance (160 N/m), and the dolomitic limestones and blast furnace slag yielded the lowest resistance (80–100 N/m), although the concretes all had similar strength properties. The fracture toughness, resistance to crack initiation, was found to be linear related with concrete strength. Typically this results in improved early age fracture toughness for concretes containing dolomitic limestone and blast furnace slag as coarse aggregate, compared to glacial gravel, because natural aggregate concrete typically has slower strength gain initially. Concrete brittleness, based on the entire load-deflection response, showed that concretes containing stronger coarse aggregate, such as glacial gravel, are significantly less brittle at early ages than are concretes containing weaker aggregate. However, these stronger aggregate concretes become more brittle, and thus crack sensitive, over time.

Life-cycle cost analysis of carbon fiber-reinforced polymer reinforced concrete bridges

This paper presents a life-cycle cost analysis of prestressed concrete highway bridges using carbon fiber-reinforced polymer (CFRP) reinforcement bars and strands. Side-by-side box beam and AASHTO beam bridge structures were considered over several span lengths and traffic volumes. The results show that despite the higher initial construction cost of CFRP reinforced bridges, they can be cost-effective when compared to traditional steel-reinforced bridges. The most cost-efficient design was found to be a medium-span CFRP reinforced AASHTO beam bridge located in a high-traffic area. A probabilistic analysis revealed that there is greater than a 95% probability that the CFRP reinforced bridge will become the least expensive option between 20 and 40 years of service, depending on traffic volume and bridge geometry. The break-even year between CFRP and steel reinforcement is typically at the time of the first major repair activity on the steel-reinforced concrete bridge.

Nonlinear aggregate interlock model for concrete pavements

The objective of the study was to develop a constitutive model that captures the nonlinear behavior of shear load transfer through aggregate interlock. A stepwise linear model was proposed. The model parameters were determined by optimizing numerically predicted to experimentally measured slab deflection basins. Continuous measurements of concrete deflection basins and truck loading were obtained using a specially designed large-scale slab tester. The numerical simulations were conducted using ABAQUS/Standard Version 6.2. Excellent deflection reproducibility was achieved for a wide range of crack widths and concrete containing different coarse aggregates. As expected, the results show that as the crack width increases, aggregate interlock is governed by the crack pattern and aggregate size. If the coarse aggregates are fractured, aggregate size does not affect aggregate interlock. The model was successfully incorporated in the pavement analysis tool EverFE 2.24 to demonstrate the significance of aggregate interlock on the efficiency of dowel retrofit across cracks. Further work is recommended on calibrating the model parameters using time-history data from falling weight deflectometer data at cracks and joints.

Performance of an AASHTO Beam Bridge Prestressed with CFRP Tendons

Corrosion-induced deterioration of steel RC highway bridges is one of the major distress types that can render a structurally deficient bridge before reaching the design life. One feasible solution to the problem is to replace the conventional steel reinforcement with noncorrosive carbon fiberereinforcedpolymer(CFRP)reinforcements.However,theCFRPreinforcementasaninternalreinforcementhasnotbeenexploredin AASHTO-typeprestressedconcretebeam bridges.AASHTO-type beamshavean I-type cross sectionwitha bottom flange, andonintegrationof thedeckslab,the finalshapeisabulb-Tsection.ThispaperdiscussestheexperimentalinvestigationofaprecastprestressedAASHTOcontrolbeam and a bridge model. A 12.5-m-long one-third scale AASHTO-type control beam was experimentally investigated for its flexural behavior when reinforcedand prestressed withCFRP. Subsequently,a one-thirdscalebridge model made of fivesuchbeamswasconstructed,instrumented,and testedunderbothserviceandultimateloadconditions.Asanticipated,thecontrolbeamandthebridgemodelfailureswereinitiatedbyrupturingof the prestressing CFRP tendons at the bottom layer. The observed flexural response of the bridge model was in close agreement with that of the controlbeam.Asexpected,thefailuremodewasprogressive,withextensivecrackingofthebridgemodel,whichgivessignificantwarningpriorto the ultimate collapse, overcoming issues related to the otherwise brittle behavior of the CFRP-reinforced structures. It is therefore highly recommendedtoprovidetheCFRPtendonsindifferentlayersalongthedepthofthebeamstoeffectivelyaddresstheissuesrelatedtobrittlefailure exhibited by CFRP reinforcements. DOI: 10.1061/(ASCE)BE.1943-5592.0000339.

Engineering Solution for the Uniform Strength of Partially Cracked Concrete

Significant computational resources are required to predict the remaining strength from numerical fracture analysis of a jointed plain concrete pavement that contains a partial depth crack. It is, therefore, advantageous when the failure strength can be adequately predicted with an engineering solution. Current engineering or closed-form solutions are based on the elastic effective crack approach with the fracture parameters toughness and critical crack tip opening of concrete. The solutions do not directly consider the effect of the distance to the boundary conditions (restrained slab length) and the cracking process caused by stress softening across the crack. A proposed engineering solution methodology includes these latter variables. The application of the solution is demonstrated on a slab containing a partial depth midslab crack and subjected to in-plane tension. The solution captures the effects of material fracture properties and structural size in terms of crack length and distance from boundary to the crack. The model assumes a bilinear stress-crack width relationship for the fracture process zone. The concrete characteristic length, determined from the fracture energy represented by the first part of the stress-crack width relationship, controls the failure load of a partially cracked concrete slab. A unique master curve between slab strength and crack depth was developed using the results from the numerical analysis. The master curve was verified with results from laboratory testing of large-scale slabs subjected to in-plane tension. The solution methodology can readily be extended to other loading cases.