Jeffrey S. West

Effect of Partial Unbonding on Prestressed Near-Surface-Mounted CFRP-Strengthened Concrete T-Beams

The flexural behavior of RC T-beams strengthened with prestressed near-surface-mounted (NSM) carbon fiber-reinforced-polymer (CFRP) reinforcement was investigated. The specific objective was to study the effect of partial unbonding of the CFRP reinforcement on the beam flexural behavior to increase the deformability. A total of eight RC T-beams were tested under four-point monotonic loading. The main variables were the level of prestressing force in the CFRP bars and the unbonded length at the midspan of the beam. The test results showed that all of the prestressed strengthened beams effectively improved the ultimate load-carrying capacity and the serviceability performance compared to the unstrengthened beam. The partially bonded prestressed beams exhibited an enhancement of the deformability compared to the fully bonded beams while minimizing the reduction of the load-carrying capacity. Partial unbonding was more effective to improve the deformability at higher levels of prestressing force. The general behavior of the partially bonded beams was reasonably well predicted by an analytical model developed previously by the writers.

Towards the classification of recycled concrete aggregates: influence of fundamental aggregate properties on recycled concrete performance

This study provides an in-depth evaluation of how fundamental aggregate properties affect mechanical properties of structural concretes produced using 100% coarse Recycled concrete aggregate (RCA) and constant mixture proportions. The key findings presented within this study will assist in developing a framework for classifying RCA sources for use in specific concrete applications. Fourteen mixture proportions were developed using three RCA types with compressive strengths of 30, 40, 50, and 60 MPa. Contrary to other studies, one RCA concrete type had compressive strengths up to 22% greater than the natural aggregate concrete. These results were confirmed by repeated batching and measured to be statistically significant. An analysis of the failure modes of RCA concrete and linking particular aggregate properties to the observed concrete failure mode were used to explain the results. Based on measured correlations, the modulus of elasticity of RCA concrete can be estimated based on the compressive strength and aggregate unit weight.

Flowing ability of self-consolidating concrete and its binder paste and mortar components incorporating rice husk ash

This paper presents the flowing abilities of various self-consolidating concretes (SCCs) and their binder paste and mortar components. The binder pastes and mortars were formulated from the concrete mixtures and tested for flowing ability with respect to flow time and flow spread, respectively, at various dosages of high-range water reducing admixture (HRWRA). The concrete mixtures were prepared with different water (W) to binder (B) ratios and rice husk ash (RHA) contents. The flowing ability of the concretes was measured with regard to slump flow, orimet flow time and flow spread, and inverted slump cone flow time and flow spread. The test results reveal that the W:B ratio, RHA content, and HRWRA dosage significantly influenced the flowing abilities of the binder pastes, mortars, and concretes. In addition, the flowing ability of the SCCs was well correlated with the flowing abilities of their binder paste and mortar components, except for the mortars including RHA.

Bond of Reinforcement in Concrete Incorporating Recycled Concrete Aggregates

Using recycled concrete aggregates (RCAs) as coarse aggregate in concrete has the potential to supplement current natural aggregate reserves, divert construction and demolition debris from landfills, and promote the adoption of sustainable civil infrastructure. As many of the design equations used to calculate structural concrete properties are based on empirical data for natural aggregate concrete, using these equations for RCA concrete may not be applicable. This study examined the bond of reinforcement in concrete produced using RCA as coarse aggregate. One natural aggregate (NA) and three RCA sources were evaluated and used as coarse aggregate in 14 separate concrete mixtures with four compressive strength levels. Various concrete mechanical properties, including compressive strength, splitting tensile strength, modulus of rupture, and fracture energy, were tested, and correlations between these properties and reinforcement bond were studied. The reinforcement bond was measured using 48 beam-end specimens incorporating several bonded lengths. The results showed that bond strength of RCA concrete was reduced by up to 21% in comparison to NA concrete, and that there was a strong correlation between bond strength and coarse aggregate crushing strength. A regression model was developed to relate bond strength to coarse aggregate strength, concrete compressive strength, and the bonded length. Using this model, experimentally predicted development lengths were calculated to be up to 9% greater for RCA concrete members in comparison to NA concrete members. Overall, this study was directed at providing guidance on the evaluation of multiple RCA sources and their respective impact on the bond of reinforcement in structural concrete.

Data Fusion Process Management for Automated Construction Progress Estimation

AbstractThis paper presents a process management framework for multisensory data fusion for the purpose of tracking the progress of construction activity. The developed framework facilitates the required type of data fusion at any given point in the construction progress, reliably and efficiently. Data are acquired from high-frequency automated technologies such as three-dimensional (3D) imaging and ultrawideband (UWB) positioning, in addition to foreman reports, schedule information, and other information sources. The results of validation through a detailed field implementation project show that the developed framework for fusing volumetric, positioning, and project control data can successfully address the challenges associated with fusing multisensory data by tracking activities rather than objects, a feature that offers superior capability, efficiency, and accuracy over the length of the project. Other contributions of this research include the development of fusion processes that are performed at hi...

Activity-based Data Fusion for Automated Progress Tracking of Construction Projects

In recent years, many researchers have investigated automated progress tracking for construction projects. These efforts range from 2D photo feature extraction to 3D laser scanners and Radio Frequency Identification (RFID) tags. A multi-sensor data fusion model that would utilize multiple sources of information would provide a better alternative than a single-source model for tracking project progress. However, the existing fusion models are based on data fusion at the sensor and object levels, and therefore, are incapable of capturing critical information regarding non-structural trades and activities on a construction site, such as welding, inspection and installation activities. This paper presents an activity-based data fusion model, which incorporates an Ultra Wide Band (UWB) positioning system to track activities in a construction project. A field experimentation study on an industrial-type building construction project was conducted to validate the model presented in this research. The scope of the experimental program was limited to ductwork, HVAC, and piping activities on the project, but the model, experiments, and results are scalable to a complete construction project. A comparison of concrete, steel, and piping projects showed that for piping projects, where the asbuilt environment may be substantially different than as-designed models, the activity-based progress estimation model of this paper can be fused with existing object-based models to provide a more accurate and reliable progress estimate.

Air Content of Self-consolidating Concrete and its Mortar Phase Including Rice Husk Ash

Abstract This paper presents the air content results of self-consolidating concrete (SCC) and its mortar phase including rice husk ash (RHA) as a supplementary cementing material. Moreover, this paper demonstrates a simple technique to determine the dosage of air-entraining admixture (AEA) required for the target air content in SCC. Different SCC mixtures were designed based on the water/binder (W/B) ratios of 0.30–0.50 and design air content of 4–8%. RHA was incorporated in the concretes substituting 0–30% of cement by weight. The mortars were formulated from the mixture proportions of the corresponding parent concretes and tested to determine the air content at various AEA dosages. The effects of W/B ratio and RHA content on the air content of both mortar and concrete were observed. The effect of mortar volume on the air content of concrete was also noticed. Besides, the AEA dosages required for the target air contents of concrete were estimated based on the equivalent mortar air contents. Later the air...

EFFECT OF OVERLOADING ON FATIGUE PERFORMANCE OF REINFORCED CONCRETE-BEAMS STRENGTHENED WITH EXTERNALLY POST-TENSIONED CARBON-FIBRE-REINFORCED POLYMER TENDONS

This paper presents the results of an experimental and analytical study of the fatigue performance of reinforced concrete beams strengthened with externally post-tensioned carbon-fibre-reinforced polymer (CFRP) tendons. Two loading conditions prior to strengthening the beams were investigated: in-service loading and overloading. A total of 18 beams were tested to failure: three under monotonic loading and fifteen under fatigue loads. The CFRP tendons were post-tensioned to 40% of their ultimate capacity. The results demonstrated that overloading the beams had no discernable effect on the fatigue life of the strengthened beams. The strain-reduction approach for unbonded steel tendons was modified to account for using CFRP tendons and for the permanent deformations resulting from the overloading process. The loading history of the beams prior to and after post-tensioning was incorporated into a strain-life fatigue model to predict the fatigue life of the strengthened beams.

Investigation of the Charlotte Motor Speedway Bridge Collapse

On May 20, 2000, shortly after the finish of a racing event at the Motor Speedway in Charlotte, NC, one span of a four-span, simply-supported, precast, pretensioned concrete pedestrian bridge collapsed injuring 107 people. The bridge was approximately five years of age at the time of collapse. Although this was a private structure used to facilitate crowd movement from the speedway to parking lots, it spanned a major US highway. The litigation that resulted from this collapse was settled over the following years. WDP & Associates, Inc. was retained by one of the principal parties in the various lawsuits and given the task to determine the probable cause of the collapse. The investigation included an extensive review of information from public and private sources; field investigation of the debris from the double-T beams that collapsed and of those that were dismantled from the other three spans did not collapse; and, an extensive laboratory investigation. This paper summarizes the investigation into the cause of the collapse. Details of the various phases of the investigation are provided. An important question that became particularly relevant during the litigation, such as whether the bridge had ever been inspected, and if it had, what was observed, is discussed.

Automated Model-Based Finding of 3D Objects in Cluttered Construction Point Cloud Models

Finding construction components in cluttered point clouds is a critical pre-processing task that requires intensive and manual operations. Accurate isolation of an object from point clouds is a key for further processing steps such as positive identification, scan-to-building information modeling (BIM), and robotic manipulation. Manual isolaton is tedious, time consuming, and disconnected from the automated tasks involved in the process. This article adapts and examines a method for finding objects within 3D point clouds robustly, quickly, and automatically. A local feature on a pair of points is employed for representing 3D shapes. The method has three steps: (1) offline model library generation, (2) online searching and matching, and (3) match refinement and isolation. Experimental tests are carried out for finding industrial (curvilinear) and structural (rectilinear) elements. The method is verified under various circumstances in order to measure its performance toward addressing the major challenges involved in 3D object finding. Results show that the method is sufficiently quick and robust to be integrated with automated process control frameworks.