Practice Periodical on Structural Design and Construction

As a result of technological progression, mathematical calculations may currently be carried out to levels of precision which are orders of magnitude greater than were possible only decades ago. Consequently, design professionals are producing structural engineering calculations to unrealistically high levels of precision. Many engineers advocate the reporting of structural design calculations to four, five, and even six significant figures, with disregard to the implicit precision on which modern design codes and specifications are based. In response to these expectations, historical documents pertaining to structural design have been reviewed, methods of structural analysis have been considered, and practical design situations have been reviewed in order to remind the structural engineer of the inherent limitations of the precision of structural engineering calculations. Conclusions have been drawn from these considerations, and a recommendation with respect to an appropriate level of precision in structural design is presented.

Integral abutment bridges provide bridge engineers with an economical and attractive design alternative to traditional bridges with thermal expansion joints. Very limited design and construction guidelines are available and no unified design procedures exist, hence there is a lack of enthusiasm to adopt integral abutment bridges for long spans. Time-dependent effects of creep, shrinkage, and temperature on composite superstructure, soil pressure from abutment backfill, and soil–substructure–superstructure interaction are the main parameters governing the design. Analytical models and numerical procedures are developed for predicting instantaneous linear and nonlinear time-dependent long-term behavior of continuous composite integral abutment bridges. The redistributions of moments due to temperature gradient, creep, shrinkage, and restraints provided by abutment foundation and backfill have been considered in the analysis. The substructure system is modeled as discrete springs for translational and rotational degrees of freedom. A numerical design example is illustrated showing the deformations and stresses due to time-dependent effects on a continuous composite deck due to typical sustained loads and compared with those of the conventional bridge system on seat-type abutments. The axial forces and moments on the piles supporting the abutment were used to analyze the behavior of the laterally loaded piles. Recommendations are presented for the analysis and design of integral abutment bridges.

The present study developed a new set of formulas for load distribution factors that are more rational than the current AASHTO LRFD formulas. A formula to quantify the intermediate diaphragm effect on live load distribution was also proposed. Preliminary coefficients of these formulas were obtained from curve fitting either with the values of AASHTO LRFD formulas or with the results from finite element modeling. The load distribution factors predicted with the proposed formulas were compared with those from AASHTO codes, field measurements, and finite element analysis with or without considering the effects of intermediate diaphragms. While the present study was intended to shed some light in developing future AASHTO LRFD design formulas, development of complete load distribution factors is out of the scope of the present study.

Delay claims are common in construction projects. Commencement delay claims are different, as the owner is responsible for the delay. This paper presents a methodology to solve the conflict of a commencement delay event in an efficient way through a case study. This paper addresses a successful commencement delay claim that a contractor solved without going through litigation. The owner refused a commencement delay claim of $2 million. There were three alternatives for the contractor: to continue the project without any claims, to go through litigation, or to settle with the owner. The contractor used a decision tree technique to minimize the cost associated with the commencement delay event. The contractor calculated the cost of different alternatives and predicted the probability of each solution. Based on the cost of each solution, the contractor selected going for a settlement with the owner for advanced payments. The present value of the settlement was $1.5 million.

The distinctive design and construction requirements of an outdoor athletic stadium in Haifa, Israel, are described in this paper. This open-air stadium accommodates approximately 2,400 seats in its upper deck, while the lower part of the stadium contains offices and visitors’ facilities. The stadium has a distinctive arrangement of 30 m high bowed-concrete columns from which 24 m long curved concrete beams are cantilevered. Because of restricted access to the project site, it was necessary to cast the stadium’s concrete columns and beams on site and then lift these elements with large cranes.

Power plants cannot function indefinitely without having to shut down one or more of the power generation units to perform major maintenance or when some type of upgrade work is necessary. These power plant shutdowns are referred to as outages and are associated with serious safety concerns that stem primarily from the fact that the workforce buildup is very fast and the work schedule is very intense. The schedule intensity is mandated by utilities that want the power plant to be fully functional as soon as possible. It is common for outage work to be scheduled with a 7 day workweek, 12 h days, and two shifts to perform this work. Research was conducted to identify those practices employed on power plant outages that resulted in low injury rates. The results showed that safer performances were associated with cost plus projects, projects where the utility financially supported safety promotion, projects where bonuses were linked to safety performance, projects that were shut down for shorter periods, projects where home office personnel gave greater support for project safety, and on projects where more innovative safety practices were implemented.

Shear lag reduces the fracture capacity of steel tension members if some, but not all, elements of the cross section transfer force at the connection. Axially loaded rectangular hollow structural sections (HSS) are commonly connected by slotting two walls and inserting a plate into the slot. The AISC Load and resistance factor design specification for steel hollow structural sections has equations to account for shear lag in slotted HSS connections. The equations are based on tests on open structural shapes. This study compares the AISC equations to the available data from previous tests and finite element models to determine whether the equations are valid for rectangular HSS members. The results of four research projects were compared to the AISC equations. The AISC equations were found reasonably accurate and generally conservative.