Saeid A. Alghamdi

A Statistical Approach to Optimizing Concrete Mixture Design

A step-by-step statistical approach is proposed to obtain optimum proportioning of concrete mixtures using the data obtained through a statistically planned experimental program. The utility of the proposed approach for optimizing the design of concrete mixture is illustrated considering a typical case in which trial mixtures were considered according to a full factorial experiment design involving three factors and their three levels (33). A total of 27 concrete mixtures with three replicates (81 specimens) were considered by varying the levels of key factors affecting compressive strength of concrete, namely, water/cementitious materials ratio (0.38, 0.43, and 0.48), cementitious materials content (350, 375, and 400 kg/m3), and fine/total aggregate ratio (0.35, 0.40, and 0.45). The experimental data were utilized to carry out analysis of variance (ANOVA) and to develop a polynomial regression model for compressive strength in terms of the three design factors considered in this study. The developed statistical model was used to show how optimization of concrete mixtures can be carried out with different possible options.

A computer algorithm for the static analysis of circular helicoidal bars

Abstract This paper presents a computer-based numerical procedure which has been devised for the static analysis of circular helicoidal bars. Based on the concepts of transfer functions, the equations of static equilibrium and deformations are formulated for a representative helicoid. These equations are then used to determine the state of stress and/or deformation at any section along the bar. In addition to its usefulness for the analysis of freely standing helicoids, and due to its systematic development, the method is particularly useful to account for the interaction between helicoidal bars and any other aggregate of structural members.

Dynamic stiffness matrix and load functions of Timoshenko beam using the transport matrix

Abstract Based on the solution of the differential equations governing the dynamic equilibrium of a Timoshenko beam, the dynamic transport matrix equations and load functions are developed. The resulting matrix equations are then used to obtain analytical expressions for the components of dynamic stiffness matrix and load functions assuming that effects of damping and cross-section warping are negligible. The resulting dynamic stiffness matrix procedure is then used to obtain the vector of dynamic stiffness load functions for beam elements subjected to concentrated and distributed loads. In terms of a characteristic ratio C r (including shear deformations and rotary inertia), the procedure is presented in a unified form by which the dynamic (or static) analysis of an integrated system of Timoshenko beams can be easily automated. Numerical implementation of the resulting dynamic stiffness matrix is verified by studying the effects of shear deformations and/or rotary inertia on values of natural frequencies for several beam cases, and one case of a rigid frame. The results obtained through application of the method of this paper are verified by comparison to results obtained by a finite element code.

The solution of differential equations governing the static analysis of a helicoidal segment

Abstract Curvilinear space bars are occasionally used in building civil and mechanical structures. For safety and/or economical considerations designers of such structures bear the responsbility of ensuring adequate performance under expected functional requirements. Under specified load conditions the appropriate analytical tools which account for all kinematic and equilibrium requirements are presented in this paper for a typical helicoidal segment as one of the more general classes of space bars. The governing differential equations of the static response of a helicoid are derived and methods of solving these equations are discussed. Finally a transport-function-based solution is presented, implemented in an example and compared with a displacement-function-based finite element solution.

Design optimization of non-uniform stiffened steel plate girders: a computer code

The paper presents a direct search design procedure that has been automated to obtain a minimum weight design of non-uniform stiffened steel plate girders. The direct search procedure does not require evaluation of design gradients and the search for minimum weight design is according to either the ASD or the LRFD design specifications of the American Institute of Steel Construction. An algorithm for the two design procedures is presented to facilitate a general utilization of the computer code. The comzputer code is tested by comparing results of minimum weight designs of a three-span stiffened steel plate girder to results obtained from a generalized reduced gradients algorithm. Results of the comparative design studies are summarized to (i) compare effectiveness of the procedure presented in this paper over a generalized gradient-based design procedure; (ii) illustrate the simplified input-output format of the computer code through a set of design examples; and (iii) compare designs obtained from the two design specifications implemented in the code.

Durability-Based Optimal Design Methodology for RC Members in Corrosive Environment

As durability-based design of reinforced concrete (RC) structures in corrosive environments is highly influenced by chloride-induced corrosion of reinforcing steel bars, this paper first presents brief outline of an experimental investigation recently carried out by the authors on a large number of reinforced concrete test specimens subjected to several scenarios of chloride-driven reinforcement corrosion. Concrete specimens were prepared with cementitious material content of 350, 375, and 400 kg/m3; water–cementitious ratios of 0.4, 0.45, and 0.5; fine to total aggregate ratios of 0.35, 0.4, and 0.45; and cover thickness of 25, 37.5, and 50 mm. The specimens were then exposed to chloride solution of three different concentrations and were tested for determining corrosionrate using electrochemical and gravimetric-weight loss methods. Numerical analysis of reinforcement-corrosion rates (determined electrochemically and gravimetrically) was first used to determine statistical correlation between corrosion rates obtained by the two methods. Then, the gravimetric reinforcement-corrosion rate results were utilized for developing regression models for reinforcement corrosion rates in terms of concrete quality parameters, concrete cover-thickness, and chloride concentration. The regression models obtained for reinforcement-corrosionrates were adapted within an automated analysis-design-methodology using Microsoft Excel solver for durabilitybased optimal design of RC members subjected to specified chloride exposure corrosive environments. Sample results obtained from the design methodology outlined in this paper are summarized for selected case studies of RC beams and columns.

Adaptive System for Assigning Reliable Students' Letter Grades—A Computer Code

The availability of automated evaluation methodologies that may reliably be used for determining students’ scholastic performance through assigning letter grades are of utmost practical importance to educators, students, and do invariably have pivotal values to all stakeholders of the academic process. In particular, educators use letter grades as quantification metrics to monitor students’ intellectual progress within a framework of clearly specified learning objectives of a course. To students grades may be used as predictive measures and motivating drives for success in a study field. However due to numerous objective and subjective variables that may by be accounted for in a methodological process of assigning students’ grades, and since such a process is often tainted with personal philosophy and human psychology factors, it is essential that educators exercise extra care in maximizing positive account of all objective factors and minimizing negative ramifications of subjectively fuzzy factors. To this end, and in an attempt to make assigning students’ grades more reliable for assessing true-level of mastering specified learning outcomes, this paper will: i) provide a literature review on previous works on the most common methods that have traditionally been in use for assigning students’ grades, and a short account of the virtues and/or vices of such methods, and ii) present a user-friendly computer code that may be easily adapted for the purpose of assigning students’ grades. This would relieve educators from the overwhelming concerns associated with mechanistic aspects of determining educational metrics, and it would allow them to have more time and focus to obtain reliable assessments of true-level of students’ mastery of learning outcomes by accounting for all possible evaluation components.

HLXVIB—A computer code for free vibration analysis of circular helicoidal bars

Abstract The development and details of the computer code HLXVIB are presented as a viable means to assess the dynamic structural response of prismatic circular helicoidal bars. To this end, the development of the dynamic transport (transfer) matrix T RL RL is first outlined for a typical helicoidal segment. Then, the implementation of the resulting matrix in the program HLXVIB is discussed to emphasize particular attractive features of the program. Several parametric studies are presented to illustrate the application of the program to studying the vibration characteristics of circular helicoidal bars as one type of the more general class of three-dimensional bars.