Journal of Structural Engineering

Full‐scale tests of cold‐formed steel C‐ and Z‐section purlins supporting conventional (through‐fastened) metal‐building roof panels were tested under gravity loading. Both single‐ and triple‐span tests were conducted on each type of purlin. Test data is presented that indicates that fastener location affects the gravity‐load capacity of C‐section purlins due to the location's effect on the torsional restraint supplied by the panels to the purlin. No effect of fastener location was noted on the capacity of Z‐section purlins. Test data are also presented that indicate that the current edition of the AISI specification (AISI: Specification 1986) overpredicts the capacity of purlins with wide compression‐flange‐stiffener lips.

Recently, a novel P‐Delta method for the design of sway frames was introduced by the writer and demonstrated in conjunction with static proportional loading conditions. The method incorporates the rigid‐plastic collapse load and the elastic buckling load of the structure as the two boundary conditions and does not require iterations or a precise trace of the load history. In this paper it is argued and verified by experiments that the P‐Delta effect for sway frames can also be predicted by the same method if loadings vary independently. Such loadings can lead to a reduced failure load compared with the static load case due to premature incremental collapse if the so‐called shakedown load is exceeded. The presented approach is a simple alternative to much more complex analysis procedures which would have to follow repeatedly the loading and unloading paths until failure is indicated. This has to be done under changing axial forces which requires iterations until the structure stiffness and the axial force level match.

A new design procedure is presented for prestressed concrete cylinder pipe subjected to internal pressure, external loads, and pipe and fluid weights based on certain limit‐states design criteria. The proposed design criteria consist of: (1) Serviceability limits for crack control in the core and the coating of the pipe; (2) elastic limits to maintain repeatability; and (3) strength limits. Design criteria for calculating combined loads and pressures corresponding to these limit states are described with the reasoning that led to their recommendation. The results of a series of carefully conducted combined‐load tests on three embedded‐ and three lined‐cylinder pipes are presented and compared to the combined loads calculated based on the proposed limit‐states design criteria. The test results show the accuracy of the proposed criteria and procedures for predicting the combined loads at first visible core and coating cracks. The actual design procedures that are used with these limit state criteria are presented in a companion paper.

A rational method for the design of prestressed concrete cylinder pipe subjected to the combined effects of external load and internal pressure is presented. This method is based on certain limit‐states criteria on serviceability, elastic limits, and strengths of the constituent materials. The design criteria and the rationale for their selection is presented in the first paper of this series. In this paper, the procedures developed for the computation of the combined loads corresponding to each design limit state are presented. The procedures include the computation of moment capacities for the thrusts resulting from prestressing and combined loads, including internal pressure, external load, and pipe and fluid weights, and a simplified method to account for moment redistribution from the invert and the crown of the pipe to the springline as the core and the coating undergo strain softening and cracking.

A complete design methodology for lightweight wooden floors must address the problem of annoying vibrations caused by occupant‐induced footfalls. Recent proposed design methods against uncomfortable floor vibrations require knowledge of the dynamic characteristics of the floor structure. Generally, these approaches require that the fundamental frequency of the floor be located outside a “human‐sensitive” frequency band. A means of accurately determining the fundamental frequency of lightweight wooden floors is thus required. This paper presents a finite strip solution procedure, adaptable to microcomputers, for the free‐vibration analysis of wooden floors. The numerical model takes into account the various complexities in lightweight wooden‐floor construction: orthotopic sheathing; variability in joist‐to‐joist stiffness; and semirigid sheathing‐to‐joist connections. A comparison against existing experimental results confirms the adequacy of this model. Using this numerical model as an analysis tool, the effects of changes in various floor parameters on the natural frequencies of wood floors is also investigated.

Virtually all structural optimizations based on system reliability were conducted considering only the ultimate state of plastic collapse initiated from the intact (i.e., undamaged) system. These single‐objective optimizations may result in decreasing the safety levels with respect to other limit states of concern, such as deformation, plastic hinge occurrences, and residual system reliability. Motivated by the need of a rational reliability‐based multilimit‐state optimization approach, where different conflicting requirements in the design of structural systems are considered simultaneously, a vector‐optimization approach is formulated. In this approach a vector‐valued objective function is examined, and the system safety is considered with regard to multiple reliability requirements imposed simultaneously. The solution to this problem is defined as the set of noninferior solutions in the space of decision variables. A three‐step reliability‐based vector‐optimization searching strategy is suggested, a decision support space is proposed, and examples of solutions for both nondeterministic truss and frame systems are presented.

The objective of this paper is to explore the potential of the lumped‐plasticity program STRUPL‐1C and to illustrate its use as a practical engineering tool for the nonlinear analysis of concrete structures. This result is achieved through the development of a moment‐rotation constitutive law that uses realistic material laws and is valid for any reinforced, prestressed and partially prestressed concrete planar frame at all behavioral states along the loading history. The effects of the main parameters that influence the moment‐rotation relationship are investigated and discussed. Finally, the developed constitutive law is applied to the nonlinear analysis of a few reinforced and prestressed concrete continuous beams. Comparison to both experimental tests and more‐complex nonlinear analysis techniques proves the accuracy of solutions obtained by the STRUPL‐1C computer program. The examples reported also prove that the proposed approach enables considerable simplification of the structural model required for a historical nonlinear analysis of concrete structures and demonstrate the high potential of the approach with respect to its use in engineering practice.

Analytical solutions for free‐vibration analysis of continuous orthotropic bridge decks are generally based on tedious numerical techniques and indirect solutions to the governing differential equation. Existing literature and results on vibration of continuous orthotropic plates is quite limited. A frequency analysis is required in order to avoid a state of resonance under live load conditions. This paper presents an empirical approach, based on the orthotropic plate theory, using a modified Levy‐type solution that draws on the principle of superposition. For the purpose of design, it is often convenient to know empirical relationships giving the range and approximate magnitude of natural frequencies. Such empirical relationships between the geometrical and structural properties of the bridge deck and associated eigenvalues are established here and presented in nondimensional form for ready reference. The solution is formulated for linearly elastic materials with isotropic or orthotropic properties and is based on the ordinary theory of thin plates.

This paper illustrates the application of a new method for performing baseline corrections on accelerograms generated by the quick‐release method. These accelerograms are produced when highway bridges are subjected to dynamic excitiations by initially deforming the structure and subsequently quick‐releasing the loads causing the deformations. In the past, the displacements caused by the quick‐release loads have not been recovered because an adequate correction procedure was not available. A baseline‐correction method was developed such that the step‐function character of the quick‐release baseline is preserved. This feature allows the complete static deformation state to be recovered by integrating the accelerograms. The power of the method is demonstrated by applying it to a suite of quick‐release data obtained during full‐scale field tests of the Meloland Road Overcrossing located near El Centro, California. As a result, complete static deformations of this bridge are obtained as a by‐product of the dynamic experiments.

Full‐ and partial‐penetration butt‐welded splices of American Institute of Steel Construction (AISC) group four and five rolled steel sections are tested. Test specimens are devised so splices are located in regions of pure bending. The partial‐penetration splice is able to develop and exceed its nominal capacity. However, it fails in a brittle manner with no apparent ductility. Qualitative explanations are given as to the cause of the observed failure. The adequacy of simple strength‐design methods to predict that behavior is assessed. Also, an example is presented for braced frames designed according to the Uniform Building Code (UBC). The acceptability of partial‐penetration welds in that design is reviewed by comparing the member forces obtained from the static analysis with those resulting from an inelastic step‐by‐step dynamic analysis. The specimen with a full‐penetration welded splice exhibits satisfactory strength and ductility. It is believed, however, that a great amount of care must be taken in the execution of this type of weld. Design implications of those results for seismic resistant structures are examined.

An investigation is conducted to determine the effects of a grit‐impregnated epoxy coating on the bond of prestressing strand. The coating is intended to inhibit corrosion, but in the process the bond characteristcs are changed. A simple test is needed for production control of the bonding capability. Fifty‐two direct tension pull‐out tests are performed on prismatic specimens made of concrete and 270‐ksi seven‐wire strand. These specimens are made with 3/8‐in. (9.5‐mm), 1/2‐in. (12.7‐mm), and 0.6‐in. (15.2‐mm) strand in an uncoated and coated condition. The 1/2‐in. (12.7‐mm) coated strand is tested with three grit densities and a coating without grit. Results indicate that the grit‐impregnated epoxy coating can provide bond strength similar to or greater than that of uncoated strand when the grit density is properly controlled. Although pull‐out specimen tests do not produce results identical to previously published values of bond stresses in the transfer length and flexural bond length of beams, they follow similar patterns. Therefore, it may be possible to develop a quality‐control test for coated strand production based on pull‐out tests.

Metal silos are subject to both internal pressure and axial compressive stresses in their cylindrical‐shell walls. Their design is often controlled by buckling. The buckling strength is greatly reduced by geometric imperfections in the wall, but increased by internal pressure. It is also increased by the stiffness of a granular bulk solid against the wall. This stiffness provides a restraint to the lower parts of funnel‐flow‐silo walls. This paper examines the elastic buckling strengths of imperfect cylindrical shells under axial compression, with imperfections in the form of a depression at a circumferential welded joint. The effects of internal pressure and elastic restraint from the static stored solid are examined. A procedure by which the characteristics of the granular solid may be incorporated into the buckling calculation is proposed. The restraint stiffness is taken to be dependent on the stress level in the stored solid, the mode of buckling, and the level of internal pressure. The results may be used in planning experiments to verify the theory, or in any assessment of the probable strength of an existing structure.

Wind pressures on buildings may be affected by various appurtenances such as mullions or vertical ribs. The determination of the influence of these appurtenances on the wind loads on cladding and structural elements of a building is important in order to identify any modifications necessary for the provisions of wind codes of practice and design standards, and also to investigate the possibility of simplification of wind tunnel building models in the event that the simulation of appurtenances appears to be insignificant to the measured wind pressures. The paper describes an experimental study carried out in the boundary‐layer wind tunnel of the Centre for Building Studies under simulated wind‐conditions over an open country and an urban terrain. The basic model of the study represents a 60.8 m by 60.8 m square building tested at two different heights (15 m and 120 m) with one‐meter and two‐meter deep mullions attached on one wall. The experimental results indicate that, in the presence of mullions, the wind‐induced suctions increase drastically at the wall edge area for almost all geometrical and exposure configurations. Trends are similar for both mean and fluctuating wind‐induced pressures. The paper quantifies these trends and makes appropriate recommendations.

Taking all cross‐sectional sizes as design variables, the paper presents a method that transforms the original optimal design model of frame structures to standard signomial geometric programming (SGP) through the generalized polynomial approach. The SGP is then solved by the condensationally based cutting‐plane method. To decrease the scale of the problem, the strength constraints are changed to size constraints by the fully stressed design method in the transformation. Several numerical examples are presented, and it is proved that this method is successful.

High‐quality optical reflector surfaces are attainable with the use of pressure‐formed membranes. The formation technique involves gradual application of fluid pressure on initially flat, simply supported circular membranes until a desirable center deflection is reached. After the fluid is removed, a uniform pressure is subsequently applied to offset the surface slope error. Empirical testing of membrane‐forming technique was conducted at two scales to define the critical process variables that controlled material yielding. Aluminum membranes with 54‐in. (1.4‐m) diameter were constructed for the smaller scale and with 144‐in. (3.7‐m) diameter for the larger scale. The experiments were carried out with the intent of forming a paraboloid with a focal length‐to‐diameter ratio of 0.6. Water or sand was used as the loading medium. Membrane surfaces with slope error less than four millirads relative to parabolic profile were achieved. The test results can be used to validate an analytical model developed to simulate the inelastic membrane deformation mechanism during free‐form yielding. With a validated model, the membrane forming process can be optimized by controlling the essential process variables identified in this study.