Finite-Element Analysis of Shear-off Failure of Keyed Dry Joints in Precast Concrete Segmental Bridges

This article has been made available through the Brunel Open Access Publishing Fund.The structural behaviour of precast concrete segmental bridges is largely dependent on the behaviour of the joints between segments. The current practice is to use small keys that are usually unreinforced, distributed over the height of the web and the flange of concrete segments and these keys are normally dry. In this study, a numerical analysis model was established based on ABAQUS finite element code to investigate structural behaviour of keyed dry joints under direct shear. The concrete damage plasticity model along with the pseudo-damping scheme were incorporated to analyse the system for microcracks and to stabilize the solution, respectively. The numerical model is calibrated by full-scale experimental results published elsewhere. It was found that the predicted ultimate load, cracking evolution history, and final crack pattern agree reasonably well with experiment results. The validated numerical model was then employed for parametric study on factors affecting shear behaviour of keyed dry joints, in this case confining pressure. It has been found that shear capacity predicted by AASHTO diverges from that predicted by numerical analysis at high confining pressure because the contribution of friction in the total shear capacity reduces with the increase in confining pressure. Hence, it is recommended to reduce the friction coefficient used in AASHTO code when high confining pressure is applied. Moreover, the propagation of inclined crack is arrested at high confining pressure due to the fact that the fracture propagation direction is governed by the criterion of the maximum energy release rate

Prototype system for knowledge problem definition

Attitudes to knowledge management (KM) have changed considerably as organizations are now realizing its benefits. Implementation, however, has been facing serious difficulties attributed to either not being able to anticipate the barriers when planning KM strategies or to using inappropriate methods and tools for implementation. These difficulties are more critical in construction due to the fragmented nature of the industry. This paper suggests that proper definition of a KM problem at the early stages of developing the KM initiatives will result in better control over the KM barriers. A methodology for identifying KM problems within a business context is then introduced. The methodology is encapsulated into a prototype software system, which facilitates its deployment in organizations and provides online help facilities. The methodology, development, operation, and evaluation of the prototype are described. The paper concludes that the prototype offers considerable potential for delivering a clarified KM problem and a distilled set of issues for an organization to address. This represents a significant first step in any KM initiative

Quality control testing for concrete during construction for a nuclear project

This paper presents the results of an oversight evaluation of qualification and production testing of concrete materials and concrete for a nuclear project in United States.  The testing requirements for qualification of concrete materials, including cement, fly ash, fine and coarse aggregates, admixtures, were in accordance with American Concrete Institute (ACI) ACI 349, ASME/ANSI and ASTM standards.  Concrete was produced from a ready mixed plant and delivered to the site in truck mixer/agitator trucks. Qualification tests for selecting concrete mix proportions for the 4000 psi design compressive strength concrete were performed, using the proposed concrete materials, in accordance with the specifications.  Qualification tests for aggregates included alkali-silica reactivity, Los Angeles abrasion, gradation, minus 200 material, moisture content, and deleterious materials, and were performed in accordance with ASTM C33 requirements.  Quality control tests for concrete during production included slump (ASTM C143), air content (ASTM C231), unit weight (ASTM C157), and compressive strength (ASTM C39).  Minimum ACI 349/ASME/ANSI N45.2.5 testing frequencies for concrete constituents and concrete are also described. Results of the QC tests including an evaluation of the 7-day and 28-day compressive strength tests are presented

Derivation of normalized pressure impulse curves for flexural ultra high performance concrete slabs

In previous studies, a finite-difference procedure was developed to analyze the dynamic response of simply supported normal reinforced concrete (NRC) slabs under blast loads. Ultra high performance concrete (UHPC) is a relatively new material with high strength and high deformation capacity in comparison with conventional normal strength concrete. Therefore, the finite-difference procedure for analysis of conventional reinforced concrete members against blast loads needs to be significantly adapted and extended to accommodate UHPC. In this paper, an advanced moment-rotation analysis model, employed to simulate the behavior of the plastic hinge of an UHPC member, is incorporated into the finite-difference procedure for the dynamic response analysis of reinforced UHPC slabs under blast loads. The accuracy of the finite-difference analysis model that utilized the moment-rotation analysis technique was validated using results from blast tests conducted on UHPC slabs. The validated finite-difference model was then used to generate pressure impulse (PI) curves. Parametric studies were then conducted to investigate the effects of various sectional and member properties on PI curves. Based on the simulated results, two equations were derived that can be used to normalize a PI curve. Further numerical testing of the normalization equations for UHPC members was then undertaken. The generated normalized PI curve, accompanied by the derived normalization equations, can be used for the purposes of general UHPC blast design.Jonathon Dragos; Chengqing Wu; Matthew Haskett; and Deric Oehler

Combining dynamic relaxation method with artificial neural networks to enhance simulation of tensegrity structures

Abstract: Structural analyses of tensegrity structures must account for geometrical nonlinearity. The dynamic relaxation method correctly models static behavior in most situations. However, the requirements for precision increase when these structures are actively controlled. This paper describes the use of neural networks to improve the accuracy of the dynamic relaxation method in order to correspond more closely to data measured from a full-scale laboratory structure. An additional investigation evaluates training the network during the service life for further increases in accuracy. Tests showed that artificial neural networks increased model accuracy when used with the dynamic relaxation method. Replacing the dynamic relaxation method completely by a neural network did not provide satisfactory results. First tests involving training the neural network online showed potential to adapt the model to changes during the service life of the structure. DOI: 10.1061/�ASCE�0733-9445�2003�129:5�672

A study of two stochastic search methods for structural control

Abstract: Many engineering tasks involve the search for good solutions among many possibilities. In most cases, tasks are too complex to be modeled completely and their solution spaces often contain local minima. Therefore, classical optimization techniques cannot, in general, be applied effectively. This paper studies two stochastic search methods, one well-established �simulated annealing � and one recently developed �probabilistic global search Lausanne�, applied to structural shape control. Search results are applied to control the quasistatic displacement of a tensegrity structure with multiple objectives and interdependent actuator effects. The best method depends on the accuracy related to requirements defined by the objective function and the maximum number of evaluations that are allowed

Monitoring Earth Pressure Balance Tunnels in Los Angeles

ABSTRACT: Tunneling using earth pressure balance (EPB) tunneling methods has been active in Los Angeles over the last seven years. Three recent large-diameter EPB tunnel projects have been completed to create approximately 32km (20 miles) of precast concrete lined tunnel excavated through alluvial soils and soft, sedimentary rock. This paper addresses monitoring of ground surface subsidence using data collected from geotechnical instrumentation and TBM performance parameters. TBM operating data are used in conjunction with surface-installed instrumentation to predict surface subsidence. TBM operations may then be adjusted to reduce potential settlementrelated damage to adjacent structures or utilities. Monitoring instruments using remote access is also addressed. The paper provides case histories of successful performance monitoring to support future urban tunneling projects