Roof Truss Research Articles

Structural Design And Analysis Of Transportable,Rapid-assembly Performance Staging

The use of structural scaffolding systems is widespread in the concert performance industry. Each year, new stage design concepts are utilized; these new concepts expand the envelope in both physical size (containing over 20,000 members) and load bearing characteristics. A stage design must be quickly assembled, while having the ability to be transportable. The desire to cut costs causes the stage designers to optimize the numbers of structural members which is used in the skeleton of the assembly. In order to determine the structural integrity of the stage design, in depth analysis is required. There is, however, a lack of complex structural analysis performed on the stage designs. Due to the large numbers of people who attend the events, and the injury potential, city inspectors and engineers are becoming very aggressive in their inspection and structural validation of the staging designs. As a result of this scrutiny, one class of concert stage design has been analyzed. The analyzed stage design incorporates a roof truss with dimensions 60 ft. by 48 ft. (18.3 m x 14.6 m); the total material weight of the roof structure is approximately 9000 Ib. (40 KN). Under nominal operating conditions, a dead load of 33,600 Ib. (149.5 KN) is supported by the roof truss. The sound wings, located on each side of the stage, must not only support the roof and lighting systems, but the wings must also support the sound equipment which has a weight of approximately 10,000 Ib. (44.5 KN). The roof grid is supported about 50 ft. (15.25 m) above the stage, by six steel cables which are hung from the sound wings. The analysis which is presented covers both dead and live loads which affect the stage. The analysis looks into the stresses placed upon the various connection schemes which are employed. As a result of this work, a complete design and analysis package is available to the staging manufacturer, validating the integrity of this class of performance staging.

The potential of press-joining in cold-formed steel structures

This paper describes a study into the potential of a new connection technique for use in coldformed steel structures. The technique, called press-joining, has many advantages over current methods. A series of small scale tests was carried out to investigate the performance in shear and bending. Comparative tests were also carried out with rivets and self tapping screws. Four full scale structural tests were carried out on pitched roof trusses using cold-formed steel channel sections.

Investigating and Repairing Wood Bowstring Trusses

A number of roof collapses in the Chicago area have been associated with the failure of heavy timber bowstring roof trusses that were constructed from the 1920s through the early 1960s in the Midwest. Based on investigation of collapsed and damaged bowstring trusses, several deficiencies and defects are common to this structural system. Performance problems are attributed to deficiencies in the original design of the trusses combined with damage due to exposure and age. The allowable tensile capacity of wood members was generally overestimated in the original design. Furthermore, unbalanced loads caused by drifting snow was generally not considered. Truss bottom chords and bottom-chord splices fail in tension, and web-member–to–chord connections are prone to fail under unbalanced loading conditions. Methods for investigating, analyzing, and designing repairs for wood bowstring trusses are presented. Building owners and structural engineers should be aware of the unique problems commonly associated with this truss type.

Innovative concept in tailgate entry support: elimination of crib blocks through utilization of new high capacity roof truss systems : J. C. Stankus, Song Guo, J. J. McCaffrey & S. S. Peng, in: Proc. 13th international conference, ground control in mining, Morgantown, WV, 1994, ed S.S. Peng, (WVU/USBM), 1994, pp 166–174

Innovative concept in tailgate entry support: elimination of crib blocks through utilization of new high capacity roof truss systems : J. C. Stankus, Song Guo, J. J. McCaffrey & S. S. Peng, in: Proc. 13th international conference, ground control in mining, Morgantown, WV, 1994, ed S.S. Peng, (WVU/USBM), 1994, pp 166–174

Effective Lengths of Uniform and Stepped Crane Columns

Crane columns are used extensively in warehouses and mill buildings to support overhead cranes. In addition to carrying the dead and live loads of the moving cranes, crane columns are required to support the roof structure of the buildings. The cross-section of a crane column can be uniform or stepped. In the former, a bracket bolted or welded to the face of the column is used to support the runway girder as shown in Figure la. In the latter, the runway girder rests directly on the enlarged segment of the column as shown in Figure lb. In earlier years, it was common practice to erect the crane column independent of the frame column. The two were then connected by batten plates or laces to act as a composite unit as shown in Figure 1c. In any case, the base of the column may be pinned or fixed. If the upper shaft of the column is rigidly connected to the roof of the building, resistance to inplane translation is provided by rigid frame action and the base of the column can be designed as pinned or fixed. However, if the upper shaft of the column is not rigidly connected to the roof as for the case when prefabricated roof trusses are used, the base of the crane column must be designed as rigid so that resistance to sway can be provided by cantilever action of the column.

Report on the Application of Finite Element Analysis to Historic Structures: Westminster Hall, London

Finite element analysis (FEA) is a computeraided modern engineering analysis technique capable of revolutionizing the practice of historic structures research. Only recently applied to historic structures, FEA is a tool available to architectural historians interested in understanding the structural logic and behavior of buildings and their component parts. The case study presented in this paper combines historical research and FEA to explore the performance of one of the greatest medieval heavy timber structures, Hugh Herland's roof trusses at Westminster Hall (1395-1396), and to assess the structural contribution of their prevalent and highly ornamental tracery. The complexity of this analysis, previously unsolvable with the tools available to historians and engineers, provides an excellent opportunity to demonstrate the capacity of FEA working in concert with historical research to clarify structural issues and reveal insights into the construction, longevity, and possible origins of historic structural types. At Westminster Hall we find that the tracery in Herland's trusses performed the role of reducing bending stresses in the principal members and, as a secondary structural system, was responsible for maintaining the structural integrity of the roof over time. These non-aesthetic functions may well have been understood by the designer.

Practical Approaches in Mill Building Columns Subjected to Heavy Crane Loads

Since the turn of this century, the amount of analytical and experimental research in the area of column design has been extensive. While the information and results of such research is scattered and narrowly focused in very specialized areas, identification of this vast amount of relevant information available is often difficult. There is no legal code governing the design of heavy mill building columns and the designs are based on experience and judgment. Additionally, there are varying types of mill building columns due to assumptions and geometry. This has led to a design practice that varies from one designer to another, based on their experience and knowledge of the mill buildings. For a practicing engineer it is essential to analyze, integrate, and establish a logical and comprehensive design methodology and procedures. It is not possible to establish one generic approach applicable to all types of mill building columns. It is rather easier to deal independently with each type of these complex structural elements in achieving this goal. This paper presents a design methodology and procedures for "heavy mill building columns" subjected to heavy crane loads. For the purpose of this paper heavy crane loads are defined as loads imparted by cranes with lifting capacity ranges from 100 tons to 500 tons such as hot metal cranes. These columns consist of two or more shafts and are laced together to achieve composite behavior. The column bases are fully fixed and the roof trusses are simply supported at the top of the building shaft. The bottom chords of the trusses are braced the full length of the building. Other types of mill building columns are not included in the scope of this paper. Therefore, the procedures and methodology presented herein may not be directly applicable to any other type of mill building column.

Discussion of “Common Causes of Collapse of Metal‐Plate—Connected Wood Roof Trusses” by Harvey A. Kagan (November, 1993, Vol. 7, No. 4)

Discussion of “Common Causes of Collapse of Metal‐Plate—Connected Wood Roof Trusses” by Harvey A. Kagan (November, 1993, Vol. 7, No. 4)

Closure to “Common Causes of Collapse of Metal‐Plate—Connected Wood Roof Trusses” by Harvey A. Kagan (November, 1993, Vol. 7, No. 4)

Closure to “Common Causes of Collapse of Metal‐Plate—Connected Wood Roof Trusses” by Harvey A. Kagan (November, 1993, Vol. 7, No. 4)

Genetic Algorithms in Discrete Optimization of Steel Truss Roofs

Genetic algorithms have their basis in Darwin’s theory of survival of the fittest. These algorithms have been used successfully in genetics and recently in a variety of optimization problems. In this paper, the mixed layout and sizing optimization problem of a typical steel roof is solved using a genetic algorithm for the layout part, and a logic problem is used for the sizing optimization of the truss roof. The method is applied to large-design-space problems, and near-optimum solutions are found in reasonable computing time. The genetic algorithm is based on a roulette-wheel reproduction scheme, a single point crossover, and a standard mutation scheme. An elitist strategy is also used that passes the best designs of a generation to the next generation. Numerical results are presented that show the efficiency of the method. Estimates of the various parameters of the algorithm are determined, which render the method an efficient optimization method for discrete structural design problems.

Common Causes of Collapse of Metal‐Plate—Connected Wood Roof Trusses

Metal‐plate‐connected wood roof trusses are a popular structural system for light‐framed structures. They are extremely flexible and unstable until set in place and adequately braced. Though truss‐plate manufacturers have developed handling and bracing recommendations, many truss installers ignore these guidelines. This paper discusses three roof‐truss collapses that the writer has investigated and points out how the failure to properly brace the trusses is a common source of collapse. In one case, a collapse occurred twice during the truss erection. In another case, collapse occurred six years after completion. In a third case, mishandling of trusses during erection was also a contributing factor. In these cases, design and erection responsibilities were in the hands of the construction contractor. It is suggested that building‐code changes are needed to ensure that there is a rational bracing plan detailed for the use of the truss installer.

An Unusual Roof Truss for Upper Rooms with Low Side Walls

Nine buildings have been found, the majority in a small area of Gloucestershire, with a similar type of roof truss, not known elsewhere. The truss depends on a diagonal brace from the floor beam to the wall head, with no tiebeam, truncated or otherwise. All examples date from the mid-seventeenth to the early-eighteenth century.

An Unusual Roof Truss for Upper Rooms with Low Side Walls

Nine buildings have been found, the majority in a small area of Gloucestershire, with a similar type of roof truss, not known elsewhere. The truss depends on a diagonal brace from the floor beam to the wall head, with no tiebeam, truncated or otherwise. All examples date from the mid-seventeenth to the early-eighteenth century.

Flexural Strength of WT Sections

WT sections are commonly used as chord members in lightly and moderately loaded roof and floor trusses. In this application, these members are subjected to combined axial and flexural loads. The design of these sections for flexural loads was not specifically addressed in the ASD Specification. Not until the publication of the LRFD Specification was flexural loading of these sections directly addressed. With the advent of ultimate strength design methods included in the LRFD Specification, it became obvious that these sections could carry increased loads. This paper will look at design capacity for these sections and will report on laboratory experimentation supporting these limits.

Field Testing of a Metal Connecting System for ‘Bush-pole’ Trusses in Sierra Leone, West Africa

The field testing of a metal connecting system for use with round timber poles to fabricate roof trusses is described in this article. The system was used to produce trusses for the roof frame on structures in the north and south of Sierra Leone. Working within a village-based project in a developing region requires that the engineer not only be able to transfer technological skills but also be cognizant of local socio-economic, cultural, and material availability factors.

Measuring Productivity and Validating Microcomputer Simulation

Abstract: Computer simulation can provide an eficient and cost‐effective method of analyzing project alternatives, resource constraints and potential progress. It is frequently performed to study the behavior of a system in an attempt to improve performance. There are many different analytical methods that can be used to plan or analyze a construction operation. However, in most cases, analytical techniques require abstractions which tend to reduce confidence in model predictions. These methods do, however, offer a basis for validating simulation results. This paper illustrates how Micro CYCLONE, a microcomputer‐based simulation language, can be used to measure job productivity in construction. It also illustrates how BetaFit, a microcomputer‐based program, can be used to model accurately and eficiently random processes for use in the simulation experiments. The paper also presents a framework for validating construction simulation by reviewing the application of two analytical methods. A roof truss process is modeled using the CYCLONE methodology and then validated using queueing theory and method productivity delay modeling to illustrate the various procedures.

Fire‐Related Roof Collapse: Case Study

On the morning of October 2, 1982, a fire broke out at an abandoned training facility on an army base in Boston, Massachusetts. While firemen were fighting the fire from the roof, the roof collapsed, shearing the roof trusses away from the columns, and falling straight down leaving all the walls standing. Three firemen were permanently disabled, while others sustained injuries of varying severity. Because of the extra-ordinary mechanism of collapse, an investigation into the probable causes of collapse was undertaken. The building had been cleaned up immediately after the fire and no physical evidence existed, except for some photographs that were taken by an arson-squad investigator some hours after the fire. The investigation, which was begun in October of 1987, showed that the building had been moved in the late 1950s. Without any opportunity to investigate the building after the collapse, a case was made that the building had not been constructed properly, either originally or after the move, and that most likely the collapse occurred because some shear rings had been left out. After one day in court, the Federal Government settled.

扠首組の変容からみた東北地方の民家における自然災害への適応過程について

There are several types of "SASUGUMI" (Japanese style roof truss) in traditional farmhouses at TOHOKU district. We analysised the mechanical property - rigidity - of 8types of "SASUGUMI" and reached the following 3 conclusions. (1) The rigidity of "SASUGUMI" is ruled by "SASU" (like a rafter-beam) and tie beam. (2) The types of "SASUGUMI" with collar (〓) are very effective against vertical load. (3) The types of "SASUGUMI" with "tsuka" (〓) are very effective against horizontal load. At the areas with many calamities of wind and earthquake, "SASUGUMI" had been transformed to the types with "tsuka" (〓), and at the snowy areas with many calamities of wind and earth-quake, "SASUGUMI" had been changed to the types combined collar (〓) with "tsuka" (〓). So, we have reached the conclusion that "SASUGUMI" had been transformed to adaptate the natural calamities.

Optimum geometry design of roof trusses by optimality criteria method

The development of structural optimization algorithms has helped engineers to a great extent in finding the most suitable structural shape for a particular loading system. However, the common aspect of the optimum shapes obtained in the research works is that they are sometimes unacceptable from a practical point of view, particularly in the case of roof trusses. An effective optimum design method for fixed geometry has been employed to determine the most suitable shape of a root truss among the commonly used ones. The algorithm is efficient and obtains the final design in few iterations which makes the trial type of procedure feasible. After finding the suitable shape, the slope of the upper chord was changed to gain further reduction in the weight. The design method which makes use of the optimality criteria approach was later extended to include the roof slope as design variable. The demonstration of the method was carried out by considering a number of design examples.

VI. The Pilgrims' Hall, Winchester. Hammerbeams, Base Crucks and Aisle-Derivative Roof Structures

The roof of the so called ‘Pilgrims’ Hall’, Winchester, now dated to c. 1308, has long been recognized as one of the earliest surviving examples of hammerbeam construction. It is somewhat surprising, therefore, that the complete medieval structure, of which the Pilgrims’ Hall forms rather less than half, has not previously been investigated in detail. In its original form it was a six bay building covered by a single roof, which, though of one constructional phase, employed a variety of principal truss types (fig. 1). The three bays at the north end of the complex have masonry walls: they comprise the actual Pilgrims’ Hall, whose most impressive feature is its pair of hammerbeam trusses (pl. XLa). The other three bays had timber framed walls, and were subdivided into a second, two bay hall with a central base cruck truss, and a single bay at the south end of the building. In this paper the term ‘Pilgrims’ Hall’ is used to denote only the three bay hammerbeam hall, while the entire original structure is referred to as the ‘Pilgrims’ range’.The roof and timber framing of the complex must surely rank with those few structures that, in the words of the late R. T. Mason, ‘stand out for their contribution to overall knowledge’. The outstanding significance of the Pilgrims' range in the study of early medieval carpentry is that it included four major ‘aisle-derivative’ roof truss types in a single building: a true aisled truss, a base cruck truss, two hammerbeam trusses, and at least one raised aisle truss. The existence of continuous longitudinal members (arcade plates, cornice plates and a central purlin) and the uniform upper roof structure throughout the length of the range show that the entire roof was erected in a single campaign.