Enrique Hernández-Montes

AN ENERGY-BASED FORMULATION FOR FIRST-AND MULTIPLE-MODE NONLINEAR STATIC (PUSHOVER) ANALYSES

Existing nonlinear static (pushover) methods of analysis establish the capacity curve of a structure with respect to the roof displacement. Disproportionate increases in the roof displacement, and even outright reversals in the case of higher mode pushover analyses, can distort the capacity curve of the “equivalent” SDOF system. Rather than viewing pushover analyses from the perspective of roof displacement, this paper considers the energy absorbed (or the work done) in the pushover analysis. Simple relations establish an energy-based displacement that is equivalent to the spectral displacement obtained by conventional pushover analysis methods within the linear elastic domain. Extensions to the nonlinear domain allow pushover curves to be established that resemble tradi-tional first mode pushover curves and which correct anomalies observed in some higher mode pushover curves. An example illustrates the application of a modified Multimode Pushover Analysis procedure using Yield Point Spectra.

Design of Concrete Members Subjected to Uniaxial Bending and Compression Using Reinforcement Sizing Diagrams

Traditional approaches to the design of reinforced concrete members for flexural moment and axial load have emphasized analysis to determine the location of the neutral axis for a given configuration of longitudinal reinforcement and axial load. An alternate approach is described in this paper, wherein the reinforcement required to resist the specified design moment and axial load is determined as a function of the neutral axis depth. A range of neutral axis depths is considered, resulting in a number of potential design solutions consisting of different combinations of top and bottom reinforcement. These potential design solutions are portrayed graphically using a new diagram termed a reinforcement sizing diagram (RSD). The comprehensive set of solutions displayed by the RSD provides a basis for the design engineer to select a specific combination of top and bottom reinforcement to be used in a particular design. Reinforcement may be selected to minimize total reinforcement area or to accommodate nominal amounts of compression reinforcement as may be required for convenience in construction. Several examples are presented, illustrating the technique according to the assumptions adopted in the provisions of ACI 318 and Eurocode 2. The effects of optimal reinforcement on the axial load-moment interaction diagram are illustrated for one example.

Engineered Bamboo I-Joists

Many bamboo species are well regarded for their strength and rapid renewability, although the nonuniformity of bamboo poles has impeded use in developed countries. Described herein are the results of a pilot effort to develop engineered bamboo I-joists for use in common low-rise construction applications. Solid section bamboo materials were used to fabricate I-beams; flanges consisted of single-strand bamboo material and webs consisted of bamboo OSB or three-ply material. Experimental results indicate that flexural strengths were limited to 5.2 ksi (36 MPa) by the failure of the flange finger joints; shear strengths were 2.1 ksi (14 MPa) for the bamboo OSB and 3.3 ksi (22 MPa) for the three-ply web material. The modulus of elasticity averaged 2,000 ksi (14 GPa), while the shear modulus was 250 ksi (1.7 GPa) for the bamboo OSB and 140 ksi (0.94 GPa) for the three-ply material. Design values are developed from the test results following a hybrid approach based on ASTM procedures for wood I-joists and whole bamboo poles.

A New Experience: The Course of Ethics in Engineering in the Department of Civil Engineering, University of Granada

A course in professional ethics for civil engineers was taught for the first time in Spain during the academic year 2007/08. In this paper a survey on the satisfaction and expectation of the course is presented. Surprisingly the students sought moral and ethical principles for their own ordinary lives as well as for their profession. Students were concerned about the law, but in their actions they were more concerned with their conscience, aware that it can be separate from the law.

Optimal Domains for Flexural and Axial Loading

Domains associated with the optimal design of rectangular reinforced concrete sections are established according to the provisions of ACI 318 with respect to P-M coordinates using results obtained with reinforcement sizing diagrams (RSDs). Characteristics of the optimal solutions are identified for each domain, analytical expressions for the domain boundaries are established, and a two-step solution procedure is presented for optimally determining the top and bottom reinforcement required to resist an arbitrary combination of axial load and moment. Examples illustrate the application of this computationally efficient procedure to the design of columns, singly reinforced beams, and doubly reinforced beams. The optimal domains provide new insight into reinforcement requirements for beam-column sections. A design approach is presented that is applicable to both beams and columns alike. This contrasts with the variety of piecemeal approaches currently used to determine non-optimal reinforcement solutions for beam and column sections, which can involve manual iterations, charts, and trial-and-error procedures. The savings in reinforcement can be significant for sections subjected to nonsymmetric loading and provide an opportunity to improve the sustainability of reinforced concrete construction.

The Necessary Limits to Temptation: The Turnkey Project

In case of special engineering projects of important relevance it is interesting to pay attention to several possible risks; some of them are in the field of morality or ethics. Due to the social importance of these risks, additional considerations or even additional warranties are justified.

Dynamic magnification factors of SDOF oscillators under harmonic loading

Abstract The magnification factor for the steady-state response of a SDOF system under harmonic loading is described in many structural dynamics textbooks; the well-known analytical solution is easily obtained from the solution to the damped equation of motion for harmonic loading. The complete and steady-state solutions can differ significantly. An analytical expression for the maximum response to the complete solution (steady state plus transient) remains elusive; however, a simple analytical expression is identified herein for the undamped case. Differences in the magnification factors obtained for the two solutions are discussed.

Optimal design of planar frames based on approximate second-order analysis

In the analysis of steel structures, several modern codes such as LRFD and Eurocode 3 provide for second-order approximate analysis. This paper presents a method of optimization for use in design that is directed toward improving the overall stability and strength of moment-resistant building frames. The method makes use of codified expressions for approximate second-order analysis. The objective function used in the optimization is the dominant eigenvalue of the linearized buckling problem. Only a first-order analysis is required, along with the calculation of the first eigenvalue of the linearized buckling problem of the structure. This new method provides a story by story procedure that is easily visualized. Several examples are provided to illustrate applications of the procedure.

Eccentricity-Based Optimization Procedure for Strength Design of RC Sections under Compression and In-Plane Bending Moment

The strength design of reinforced concrete (RC) rectangular sections for combined compression and in-plane bending with two levels of reinforcement is indeterminate: three unknowns are to be solved, but with only two equilibrium equations; an additional condition is necessary to solve the problem. The additional condition leads to the finding of a minimum reinforcement-concrete ratio. This paper proposes a new approach based on the equivalent eccentricity of the applied compressive load. Different domains are reported, each of which is associated with given values of eccentricity and axial load. Analytical expressions for the domain boundaries are established, and a simple procedure is described to outline the conditions corresponding to the optimal reinforcement. The main advantage of this procedure is its simplicity, which allows manual computations. Some examples employing reinforcement sizing diagrams illustrate the validity of this approach.

Full and folded forms: a compact review of the formulation of tensegrity structures:

This piece of work presents a simple and compact overview of the design problem of tensegrity structures in two and three dimensions. The main aim of this study is to present the design and calculation of tensegrity structures in their simplest form, avoiding unnecessary simplifications that can rule out solutions, as has happened up until now. As a result of the simplicity of the procedure, two types of tensegrity structures are obtained for the same initial topology: full and folded forms. Several examples are shown.