Combining hygrothermal and corrosion models to predict corrosion of metal fasteners embedded in wood

A combined heat, moisture, and corrosion model is presented and used to simulate the corrosion of metal fasteners embedded in solid wood exposed to the exterior environment. First, the moisture content and temperature at the wood/fastener interface is determined at each time step. Then, the amount of corrosion is determined spatially using an empirical corrosion rate model and the inputs of the first step. The result is a corrosion profile along the length of the fastener generated by summing the corrosion depths determined at each time step. We apply the combined model to predict the annual corrosion depth along a metal fastener in wood decks situated in nine different US cities. Corrosion profiles are found to exhibit the same general shape independently of climatic load, with the largest amount of corrosion occurring at 1–5 mm from the wood surface with corrosion depths ranging from 5 μm in Phoenix, Arizona to 45 μm in Hilo, Hawaii. Corrosion is confined to the first 7–20 mm of the fastener below the wood surface. By varying the climatic loads, we find that although there is a definite relation between total annual rain and total annual corrosion, under the same rain loads corrosion is higher for a climate with more evenly distributed rain events. The proposed combined model is able to capture corrosion behavior under varying loading. A sensitivity analysis gives guidelines for future corrosion modeling work for fasteners in wood.     

Durability Gap Analysis for Fiber-Reinforced Polymer Composites in Civil Infrastructure

The lack of a comprehensive, validated, and easily accessible data base for the durability of fiber-reinforced polymer (FRP) composites as related to civil infrastructure applications has been identified as a critical barrier to widespread acceptance of these materials by structural designers and civil engineers. This concern is emphasized since the structures of interest are primarily load bearing and are expected to remain in service over extended periods of time without significant inspection or maintenance. This paper presents a synopsis of a gap analysis study undertaken under the aegis of the Civil Engineering Research Foundation and the Federal Highway Administration to identify and prioritize critical gaps in durability data. The study focuses on the use of FRP in internal reinforcement, external strengthening, seismic retrofit, bridge decks, structural profiles, and panels. Environments of interest are moisture/solution, alkalinity, creep/relaxation, fatigue, fire, thermal effects (including freeze-thaw), and ultraviolet exposure.     

A novel approach to estimate the wind uplift resistance of roofing systems

Roof wind design consist of three parts: determination of wind loads, evaluation of wind uplift resistance and correlating the resistance with the design load such that the resistance is higher than the load requirement. Wind uplift resistance of a system with its respective components is evaluated in laboratory testing. This paper presents a novel approach to estimate wind uplift resistance when components are substituted during field application. Wind dynamics, on a mechanically attached single-ply roofing assembly, lift the membrane and cause fluttering, introducing stresses at the attachment locations. In such assemblies, the fastener–deck interface is a critical design factor. First, by taking steel deck as a component this paper systematically characterizes the various steel decks that are commonly used in low slope application. Second component, namely the fasteners and its engagement strength with deck have been quantified for variations of its design, size and sources. Based on this component characterization, fastener pullout resistance (FPR) is identified as a verification factor for system wind resistance estimation. When variations occur in the fastener–deck interface between the proposed and the existing configurations, the present research through case studies has proved that: “as long as the FPR of the proposed configuration is higher than the existing configuration then wind uplift ratings can be maintained”. This is valid as long as both the configurations have all the remaining roofing components similar with comparable layout. Based on this verification, the study recommends that the testing lab should report the FPR along with the wind uplift resistance such that FPR can be used as a verification factor to accept design/field alternatives.     

Performance Evaluation of Precast Posttensioned Concrete Multibeam Deck

An innovative bridge construction utilizing on-site posttensioned precast concrete beams that are compressed together with full depth grouted shear keys and transverse posttensioning is the subject of this paper. In particular, the performance of the shear keys with regard to load transfer and water tightness constitutes the main issues of investigation. This paper presents the results of a live load testing program and associated finite-element analysis results of the as-built bridge. Live truck load test results help provide insights on the lateral (transverse direction) load distribution characteristics among the interconnected beams. The measured lateral distribution of the applied truck load among adjacent beams showed that the load was transferred primarily to the beams close to the truck load position, validating the effectiveness of the shear key details in transporting loads.     

Fatigue Evaluation of Rib-to-Deck Welded Joints of Orthotropic Steel Bridge Deck

This study reported fatigue test results of 300-mm-wide specimens with three details: 80% partial joint penetration (80%PJP), weld melt-through (WMT), and both. The specimens were cut out from full-scale orthotropic deck specimens of 16-mm-thick deck plate. In the fatigue test, the deck plate was subjected to cyclic bending loading and the rib was free from loading. The fatigue fracture surfaces showed that the presence of WMT may affect the initiation of fatigue cracks. A propensity to root cracking rather than toe cracking was observed. Plotting fatigue test results in an S-N diagram showed that the specimens with WMT seemed to have slightly lower fatigue strengths than the 80%PJP specimens, but the difference is more likely to be within a usual scatter of test data, which means that both details have comparable fatigue strength. The present test results satisfied the S-N curves of JSSC-E (80?MPa at 2×106 cycles) or AASHTO-C (89?MPa at 2×106 cycles).     

Detection of Stiffness Reductions in Concrete Decks with Arbitrary Damage Shapes Using Incomplete Dynamic Measurements

A new refined nondestructive evaluation technique for concrete decks with arbitrary damage shapes is presented, and its utility in detecting the location and extent of the damage using only a single dynamic measurement signal is demonstrated. Six unknown parameters are considered to determine the damage distribution, which is a modified form of the bivariate Gaussian distribution function. Using a combination of the combined finite-element method (FEM) and the advanced uniform microgenetic algorithm, the various influences of different measurement locations on the damage detection are studied. In addition, the effect of noise is simulated in order to study the influence of the measurement errors and the uncertainty of the method. The sample studies demonstrate the excellence of the proposed method from the standpoints of its computation efficiency as well as its ability to investigate the complex distribution of an arbitrary stiffness reduction.     

Assessment of Seismic Performance of Two Pile-Deck Wharf Connections

This paper examines the seismic response of two full-scale pile-to-deck connections of marginal wharves built in the 1980s at the Port of Los Angeles. The first test represented a precast pretensioned concrete pile-deck connection at Berth 145. This berth required extending the deck for a new crane rail and a new line of piles. The proposed wharf upgrade considered leaving the existing piles if their lateral displacement capacity exceeded the expected seismic demands. A representative connection was tested to assess the rotation capacity under reversed cyclic loading. The second test represented a typical steel pile-deck connection used in Berth 226. In this structure, the piles support a crane rail. A reversed cyclic loading test was also conducted to assess the connection deformation capacity. Both connections were able to carry the imposed axial load throughout, even when the flexural strength had degraded. The precast pile-deck connection maintained the flexural strength up to a rotation of 0.04?rad, and the steel pile-deck connection maintained its flexural strength up to a rotation of 0.015?rad.     

Reliability Analysis of Plank Decks

The objective of this study is to summarize the load and resistance criteria for highway bridge plank decks, and to estimate the reliability of plank decks designed by the AASHTO Code. Both transverse and longitudinal planks for a variety of typical stringer spacings and plank sizes are considered. Truck traffic load data are based on the model used to calibrate the 1994 AASHTO LRFD Code. However, for plank decks, wheel load rather than whole vehicle weight is most important, and these statistics are developed for this study. For wood planks, dead load and dynamic load are not significant. The limit state considered is flexural strength, and resistance statistics are presented for wood planks in terms of modulus of rupture. Special flat-wise use data are presented to account for section aspect ratio as well as edge of load application. The reliability analysis is carried out using the procedure developed for calibration of AASHTO LRFD. Reliability indices for both the AASHTO Standard and AASHTO LRFD Code are presented for plank decks. The results indicate that there are considerable differences in plank reliability indices. Causes of inconsistencies in safety are identified.