ASCE Guidelines Research Articles

Seismic Assessment of Steel-frame Buildings Mounted with Base-Isolated System

A multi-Storey steel frame building against earthquakes has always been a challenge for structural engineering and researchers. Many seismic protection systems have been investigated overtime where the Base Isolation system has widely been used and implemented. It works on the principle of dissociation of substructure to the superstructure. In the present paper, different multi-storey steel frame buildings are evaluated, which are mounted with Lead Rubber Bearing (LRB) as a base isolator. LRB has been designed in compliance with the FEMA and ASCE guidelines. Further, a relative study is presented for evaluating the traditional fixed-base structure with a base-isolated building by performing a time history analysis. Base shear, inter-storey drift, acceleration, and displacements are examined as a result of the study. The outcome shows significant contributions towards reducing acceleration, inter-storey drift and base shear distributed over the floors. Moreover, LRB not only absorbs the seismic energy but also substantially decreases the destructive effect during an earthquake.

Frequency Domain Analysis of Alongwind Response and Study of Wind Loads for Transmission Tower Subjected to Downbursts

Downburst is one of the high-intensity winds that cause transmission tower failures. The regulations of transmission tower-line systems under downburst wind loads cannot meet the design requirements at present. In this paper, the calculation formulas of the background and resonant components of transmission tower under downburst wind loads are obtained, based on the modal analysis theory of non-stationary wind for the single-degree-of-freedom system in the frequency domain. The effects of structural dynamic characteristics, damping ratio, and mean wind speed vertical profile on dynamic effect on structural response are discussed. Then the equivalent static wind load (ESWL) is obtained according to the maximum response and compared with the finite element method (FEM) in the time domain. Applications of these formulas are addressed to the cases from the empirical model of Holmes and field record of a rear flank downdraft (RFD). The results show that the maximum responses obtained by the current formulas match well with those from the modal decomposition method and dynamic analysis with FEM. The internal forces of tower members calculated by ESWL based on maximum response are closer to the results from FEM than those calculated by downburst loads recommended in ASCE guidelines. The presented framework can be used to assist the wind-resistant design of transmission towers considering downburst wind load.

A New Formulation for Establishing the Lateral Interaction Between Buried Steel Pipeline and Sandy Soil Subjected to Strike-Slip Faulting

AbstractBuried pipelines are faced with and vulnerable to extreme hazards such as earthquakes, different types of faulting, and landslides. Generally, a buried pipeline is modeled as a beam on a series of springs, which represent the surrounding soil. To determine the specifications of these springs, the equations proposed by ASCE Guideline are usually used. Its accuracy was doubted by some recent studies. In this study, two full-scale tests simulating the effect of strike-slip faulting were initially carried out on 4 and 8-in. diameter steel pipes buried in compacted sandy soil. The displacement of the pipe was recorded directly at any moment, along its length. Then through optimization-based simulations, the specifications of the equivalent springs of the soil were calculated so that the deformation of the pipe along its length would be consistent with the experimental results. Then, based upon verified finite element models, a database of different parameters of buried pipes subjected to strike-slip faulting including the diameters and different burial depths was created. The results showed that the ASCE equations need modification at the condition of strike-slip faulting and so, based on the created database, a new form of the equations of lateral interaction between dense sandy soil and steel pipe in the presence of strike-slip fault was proposed.

New Method to Evaluate the Buried Pipeline– Sandy Soil Interaction Subjected to Strike Slip Faulting

ABSTRACT The aim of this study is to provide a new method to assess the interaction between sandy soil and buried pipeline in the presence of strike slip faulting. To that end, two full-scale experiments were carried out on steel and polyethylene pipes. Using ABAQUS and an optimization algorithm, the stiffness of the equivalent transverse spring of the soil was calculated so that the deformation of the pipe would have the highest agreement with the experimental results. The results showed that the specifications of the equivalent pipe-soil spring are highly dependent upon the material of the pipe, a fact which has not been considered in design codes. The initial stiffness and the maximum pipe-soil interaction force for both the steel and polyethylene pipes were calculated and compared to the criteria presented by ASCE and ALA standards. The maximum pipe-soil interaction force in steel pipe test was obtained to be 70% higher than ASCE Guideline given value while in HDPE pipe test it was about 80% lower than code’s value. This fact demonstrates the importance of pipe material on lateral pipe-soil interaction.

Finding Critical Element in the Progressive Collapse of RC Structures Using Sensitivity Analysis

Failure of some elements in the structure can play triggering role for beginning of collapse progression. The critical element is the structural element that when it fails, leads to progressive collapse. To find the critical element of the structure, sensitivity analysis should be done. But there are not specific structural criteria for using in sensitivity analysis. In this paper following GSA, UFC 4-023-03 and ASCE guidelines, sensitivity analysis has been modified and applied to find the critical element of a major number of reinforced concrete structures. 1080 3D nonlinear pushdown analyses were done and the results showed that the place of the critical elements differs in different stories and different plan shapes of high rise structures. In the structures with high aspect ratio in height, the critical element of the whole structure is located in the story of 2/3 height of the structure. When the aspect ratio of the structure in plan increases, sensitivity of the columns in the long dimension of the structure become closer to each other.

Mechanical response of buried High-Density Polyethylene pipelines under normal fault motions

Permanent ground deformation is one of the most damaging hazards for continuous buried lifelines. In this paper, numerical models using a Finite Element Method (FEM) were developed to analyze the buried High-Density Polyethylene (HDPE) pipelines subjected to the normal fault motions. The numerical predictions, were compared with those from ASCE Guidelines and with the experimental results obtained from geotechnical centrifuge tests. Moreover, the paper focuses on the effects of the design parameters such as, pipe diameter and thickness, pipeline burial depth, friction angle and density of the soil surrounding the pipe on the maximum bending strain as well as bending strain distribution along the pipeline. The results show that numerical models using a finite element method could produce reasonable predictions. However, the maximum predicted bending strains from the ASCE Guidelines are larger than those from experiments. The pipe deformation mechanisms are also significantly influenced by variation in burial depth, pipe surface characteristics, and backfill type.

Students’ Recommendations for the Guidelines for Failure Investigation

This is the first publication of a series of forum papers to be published by the Committee for Forensic Investigations CFI of the Technical Council on Forensic Engineering TCFE in the Journal of Performance of Constructed Facilities as part of the review and revision process of Guidelines for Failure Investigation published by ASCE’s Task Committee on Guidelines for Failure Investigations of the Technical Council on Forensic Engineering . The intent of this publication series is to keep a record of the review process and to encourage the practicing community—who may not be members of the committee—to provide feedback and comments. Consistent with the goal of any ASCE guideline, this publication is not intended to be a standard for engineering practices and is not intended for use as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. The purpose of the original Guidelines for Failure Investigation the guidelines is to provide an overview of the function and tasks for conducting a successful failure investigation. The guidelines covered aspects of the investigative process from the planning of an investigation, the development of a failure hypothesis, and the preparation of a concise report, to the engineer’s role as an expert witness. The guidelines not only provide an introduction to the investigative process for the initiate forensic engineer, but also supply the veteran investigator with references and guidance.

Safe Scaled Distance for Masonry Infilled RC Frame Structures Subjected to Airblast Loads

Terrorist bombing and accidental explosion may generate extreme loading conditions on nearby structures, resulting in damage and even collapse of structures. The degree of damage to a structure depends on the capacity of the detonation and its location as well as structural conditions. Some guidelines are available to assess the safety of unstrengthened buildings to airblast loads. These guidelines are usually given in terms of the safe scaled distance between explosion center and structure, whereas the structure conditions, which also affect its performance, are not explicitly defined. The safe scaled distance is obtained primarily from field blasting tests and experiences of structure damage to blast loads. These guidelines can be used for a quick safety assessment of structures, but do not provide clear damage scenarios of the structures. In a previous paper, damages of low-rise masonry infilled reinforced concrete (RC) structures to surface explosion of different scaled distances are numerically simulated. It was found that RC frame would collapse when the scaled distance was less than 1.82 m/kg 1/3 ; and the front masonry wall would suffer excessive damage when the scaled distance was less than about 4.5 m/kg 1/3 . The present paper is an extension of the latter work. It employs a more detailed RC model with distinctive definitions of concrete and reinforcement material performance. More thorough analyses are carried out to find the correlation between the scaled distance and the damage level of low-rise and medium-rise masonry infilled RC frames. The different failure mechanisms between the low-rise and medium-rise structures to blast loads are also observed and discussed. The computer program LS-DYNA3D with user defined RC and homogenized masonry material models is used in numerical calculations. The numerical results are also compared with the safe scaled distance recommended in the United Stated Department of Defense's regulations, ASCE guidelines, and those derived in the previous paper.

콘크리트 기둥과 철골 보 합성골조 접합부에서의 지압강도

A bearing failure in RCS(Reinforced Concrete Column and Steel Beam) system is recognized as one of the distinct joint failure modes for the composite frames. Vertical and transverse reinforcement in addition to concrete are effective for better transfer of vortical forces through concrete bearing. To examine the effect of the vertical bars, tie bars, a U-type detail developed in this study and concrete confinement, local bearing tests were conducted using 22 small-scale concrete block specimens. Test results show that vertical reinforcement and tie bars mainly contribute to the bearing capacity. However larger amounts of tie reinforcement are required than those recommend from ASCE guidelines, to apply the nominal concrete strength as 2 over the bearing area. Cross ties are proved to be highly effective for resisting the vertical forces. Maximum bearing strength can be increased upto 2.5 . An accurate prediction model for bearing strength is proposed for better design of the composite Joint.

Program for Implementation of ASCE Salary and Fringe Benefit Guidelines

The Los Angeles Section of ASCE initiated a program in 1974 and 1975 to implement salary and fringe benefit guidelines. A salary survey in the geographical area encompassed by the Los Angeles Section was conducted as a basis for comparing actual prevailing salaries with ASCE guidelines. Salary comparisons were also made with other types of employment and implementation problems were defined. Reports comparing actual salaries with ASCE guidelines were distributed in both 1974 and 1975 to major employers of civil engineers, both public and private, in the Los Angeles geographical area and also to collective bargaining units. Presentations covering the comparison of salaries and fringe benefits with ASCE guidelines were made to the section, geographical branches, and technical groups as an integral part of implementation efforts. A continuing program in coordination with the other four California ASCE Sections aimed at implementing ASCE guidelines was formulated.

ASCE's Guidelines for Participation in Public Affairs Activities Four Years Later

During the four-year period since the original guidelines were published, certain significant trends emerged in the United States. A heavy recession set in, accompanied by an ever increasing pattern of inflation accelerated by a large oil price increase by the OPEC nations. Although most civil engineers were fairly well insulated from the effects of the recession with generally high levels of employment maintained, the rest of the country was not so fortunate. Unemployment rose steadily to over 9% and economic and fiscal experts were mystified as to how to control deepening recession combined with increasing inflation. During this period, as an unrelated action, the Federal government undertook and implemented a strong affirmative action program.