Sami W. Tabsh

PROBABILISTIC MODELS FOR RESISTANCE OF CONCRETE BRIDGE GIRDERS

Resistance (load-carrying capacity) parameters are important in the development of the new generation of probability-based load and resistance factor design (LRFD) codes. Bending and shear resistances are considered for concrete bridge girders. Two structural types are considered: reinforced concrete T-beams and prestressed concrete AASHTO-type girders (American Association of State Highway and Transportation Officials). Bending capacity is calculated using well-established models for flexural behavior of reinforced concrete and prestressed concrete beams. Shear capacity is modeled using the modified compression field theory. Material properties, dimensions, and accuracy of the analytical model are treated as random variables. Statistical parameters are determined on the basis of the available test data by simulations. The calculations are performed for selected sections and spans. The simulation results serve as a basis provided to determine the bias factors and coefficients of variation of resistance. The resulting statistical parameters of resistance are summarized in tables.

CONFINEMENT OF HIGH-STRENGTH CONCRETE WITH WELDED WIRE REINFORCEMENT

This paper describes an experimental study, involving the testing of 14 full-size high-strength concrete columns in axial compression, conducted to determine the effectiveness of using 2D welded wire reinforcement (WWR) grids as transverse reinforcement in the columns. The performance of columns laterally reinforced with WWR was compared with that of columns laterally reinforced with conventional ties. Axial stress-strain diagrams of the concrete core from the experimental tests showed that substantial gains in strength and ductility of columns laterally reinforced with WWR can be achieved if the volumetric ratio of transverse steel was above 3.5%. Strength increases of at least 15% were observed, while ductility increases of 250%+ were recorded in the specimens with WWR when compared with the corresponding specimens with conventional ties.

Faculty response to ethical issues at an American university in the Middle‐East

Purpose – The objective of this study is to get feedback on faculty perception of ethical issues related to teaching, scholarship and service at a relatively new American‐style university in the Middle‐East.Design/methodology/approach – A questionnaire involving 21 scenarios with multiple choice answers was developed and distributed to all faculty at the institution to get their opinion on the issues. The effects of faculty background, gender, rank, and administrative responsibilities on the obtained responses at the institution were considered.Findings – The findings include: about one‐third of the faculty participants were unaware of the universitys code of ethics; several of the faculty surveyed stated that they would ignore violations of an ethical code of conduct committed by colleagues; and there was no definite trend observed between the responses of faculty based on their discipline.Research limitations/implications – The study is based on a questionnaire; this implies that the faculty responses ...

Structural Capacity Reduction for Drilled Shafts with Minor Flaws

In the last decade, use of drilled shafts has increased due to their cost-effectiveness, versatility, and minimal environmental impact compared with other types of deep foundations. The construction process, however, sometimes introduces minor flaws that are not always detectable with well-performed nondestructive evaluation (NDE) processes. The construction method, working environment, and visibility of the end product for drilled shafts are different from those of an element in the superstructure, yet most structural designers typically attempt to ensure safety in both types of elements using the same resistance factors. This paper summarizes results of a comprehensive series of research projects involving flawed drilled shafts and investigates the frequency of occurrence of flaws that will not normally be detected by well-executed NDE programs. The results from this study present capacity reduction factors corresponding to worst-case scenarios. These factors should be refined using a probabilistic approach to formulate realistic resistance factors to be used in the structural design of drilled shafts considering the presence of undetectable minor flaws.

Review of Research on and Implementation of Recycled Concrete Aggregate in the GCC

The goal of sustainable construction is to reduce the environmental impact of a constructed facility over its lifetime. Concrete is the main material used in construction in the Gulf Cooperation Council (GCC). Therefore, it makes economic and environmental sense to use recycled materials in the making of new concrete for different applications. The objectives of this study are to summarize published research on the use of recycled concrete aggregates in new concrete mixes and examine its implementation in construction and industry in the GCC region. The study showed that while there is reasonable research on recycled concrete, the practical implementation in the region greatly lacks behind, especially due to the lack of economic viability and awareness of such applications at the current time.

STRUCTURAL SAFETY OF POST-TENSIONED CONCRETE SLAB BRIDGES WITH UNBONDED TENDONS

The authors examine the structural safety of simply supported post-tensioned concrete slab bridges with unbonded tendons. Slab designs are in accordance with the American Association of State Highway and Transportation Officials (AASHTO) load factor design specifications, and service stresses and ultimate strength are both considered in the design. Probabilistic resistance models that consider variabilities in material properties and section dimensions are developed using simulation methods. Reliability for flexural capacity at ultimate limit state is measured in terms of the reliability index. Sensitivity analysis is conducted to study the effects of changes in span length and prestressing steel reinforcement ratio on stress in unbonded tendons, bending moment capacity, and reliability index. Results of the analysis revealed that statistical properties of bending moment capacity at ultimate are a function of the amount of prestressing steel. Furthermore, designs based on current AASHTO specifications result in considerable nonuniform safety for bridges having different span lengths and reinforcement indexes.

Utilization of Recycled Coarse Aggregate in Concrete Mixes

In this paper, the effect of the source of recycled coarse aggregate on the properties of concrete is investigated. The tests were conducted on concrete made from three sources of recycled aggregates: (1) old concrete with unknown strength, (2) old concrete with a known compressive strength of 21 MPa, and (3) old concrete with a known strength of 42 MPa. The three sources of recycled aggregates were used to produce new concrete with a target compressive strength of 21 MPa. The first and third sources of recycled aggregates were used in producing concrete with target strength of 42 MPa. A control mix was designed with aggregates from natural sources. The research included two methods of making recycled concrete. One concrete mix was produced using the recycled aggregate and adding more water than the control mix, to reach the target slump, while the second concrete mix was produced using the same amount of water as the control mix but with additional superplasticizer to maintain the target slump. The results obtained in this research showed that the concrete compressive strength depends on the source of recycled aggregates; the stronger the source of recycled aggregate, the higher the compressive strength of the produced concrete. Furthermore, the compressive strength of the first concrete mix was about 10%-20% lower than the compressive strength of the control mix. However, when superplasticizers were used, the compressive strength was around the same value as the control mix.

Engineering students and faculty perceptions of academic dishonesty

Purpose This paper aims to survey students and faculty from the College of Engineering at an American university in the United Arab Emirates about their perception on different issues related to academic dishonesty. Opinions were sought on plagiarism, inappropriate collaboration, cheating on exams, copyright violations and complicity in academic dishonesty. Reasons for students to commit dishonest acts and ways to reduce academic misconduct were also included. Design/methodology/approach A survey involving 11 questions with multiple choice answers was developed and distributed to engineering students and faculty at the institution to get their perception of the considered issues. Findings Results of the study showed that while faculty and students were generally in agreement in their perception of the frequency of academic dishonesty among students, they greatly differed on the courses of action needed to reduce them. Most faculty members favored applying tougher penalties and using more proctors in exams. On the other hand, students preferred softer approaches such as educating them on academic integrity issues, applying lenient deadlines for assignments and reducing the difficulty of exams. Research limitations/implications The conclusions and recommendations of the study are applicable to colleges of higher education having similar characteristics and culture to the surveyed institution. Practical implications The findings can be used to understand students’ behavior and faculty’s attitude toward academic dishonesty, and to assess the effectiveness of current strategies addressing the issue at similar universities in the region. Originality/value The conducted literature review indicated that this work is believed to be a pioneering case study in the Gulf Cooperation Council countries.