The authors address a myriad of topics, covering both traditional and innovative approaches to analysis, design, and rehabilitation.
The second edition has been expanded and reorganized to be more informative and cohesive. It also follows the developments that have emerged in the field since the previous edition, such as advanced analysis for structural design, performance-based design of earthquake-resistant structures, lifecycle evaluation and condition assessment of existing structures, the use of high-performance materials for construction, and design for safety. Additionally, the book includes numerous tables, charts, and equations, as well as extensive references, reading lists, and websites for further study or more in-depth information.
Emphasizing practical applications and easy implementation, this text reflects the increasingly global nature of engineering, compiling the efforts of an international panel of experts from industry and academia. This is a necessity for anyone studying or practicing in the field of structural engineering.
New to this edition Fundamental theories of structural dynamics Advanced analysis Wind and earthquake-resistant design Design of prestressed concrete, masonry, timber, and glass structures Properties, behavior, and use of high-performance steel, concrete, and fiber-reinforced polymers Semirigid frame structures Structural bracing Structural design for fire safety.
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This edition doesn't have a description yet. Can you add one? Add another edition? Copy and paste this code into your Wikipedia page. Need help? Guide for design of steel transmission towers prepared by the Task Committee Donate this book to the Internet Archive library.
If you own this book, you can mail it to our address below. Not in Library. Want to Read. Generally, guyed towers are used in flat to rolling terrain. They can be used in rough terrain if guy slopes are sufficiently steep so that the downhill guy leads are not excessively long 2.
Horizontal bracing is also used in square and rec- tangular towers and masts to support horizontal struts and to provide stiffer structures to assist in reducing distortion caused by oblique wind loads. Horizontal bracing is normally used at levels where there is a change in the slope of the tower leg to assist the bracing system in resolving the horizontal component.
In square and rectangular towers it is not unusual for the structure to extend 75 ft from the foundation to the first panel of horizontal bracing. The cross section of the tower, the stiffness of the lacing members, and the torsional load distribution normally determine how often horizontal cross-bracing is required. For structures with a square or rectangular configuration greater than ft high, or heavy dead-end towers, it is suggested that horizontal bracing be installed at intervals not exceeding 75 ft.
The spacing of horizontal bracing is dictated by general stiffness requirements to main- tain tower geometry and face alignment. Factors which affect this deter- mination are type of bracing system, the face slope, the dead load sag of the face material, and erection considerations that affect splice locations and member lengths.
Alpert, S. Behncke, R. Bergstrom, R. Hoffman, G. Marsico, R. Petersen, W. Sansom, H. Wood, D. Moments normally exist in members of a tower because of framing eccentricities, slightly eccentric loads, lateral wind load on members, etc. Since moments are small and it is impractical to model every eccentric detail, towers are analyzed almost exclusively as ideal trusses, i. These analyses produce only joint displacements, tension or compression in members, and tension in cables.
For other shapes framing eccentricities must be considered in the design of the members. Because of the high degree of sym- metry of most towers, a transverse view, a longitudinal view, and a few horizontal cross-section or plan views are sufficient to describe the entire structure. For purposes of analysis, a tower can be represented by a model composed of mem- bers and sometimes cables interconnected at joints.
Members are nor- mally classified as primary and secondary also called redundant mem- bers. Primary members form the triangulated system three-dimensional truss that carries the loads from their application points down to the tower foundation. Secondary members are used to provide intermediate bracing points to the primary members and thus reduce unbraced lengths of the primary members. In Fig. The forces in the secondary members are equal to zero in a linear first-order truss analysis.
Therefore, simplifying assumptions were made in order to reduce the analysis of a tower to independent analyses of several statically determinate plane trusses. These assumptions are well described in classical textbooks on structural analysis and in Marjerrison and Zar and Arena These simplified analyses algebraic or graphical require that the analyst visualize the load path through the determinate plane trusses. While the graphical method force diagram is time-consuming and somewhat limited to simple configurations, it provides the designer with a very good feel for how the tower behaves and how the bracing functions under each type of applied load 3.
Redundant members need not be included in this type of analysis since they have no effect on the forces in the load-carrying members. This type of analysis is generally used for self-supporting latticed towers. Some analysts assume that the member is still capable of carrying its buckling load irrespective of the amount of strain beyond ena, Fig.
The process requires a certain number of iterations to determine which bracing members are loaded beyond their compression capacity and to remove such members from the model, thus forcing the remaining bracing members to carry the load in tension.
In building frameworks and flexible pole structures this is called the PA effect. A second-order or nonlinear in the geometric sense analysis is one that produces forces that are in equilibrium in the deformed geometry. A nonlinear analysis is normally performed as a succession of first-order analyses; the geom- etry of the structure is updated at the end of each iteration Peyrot ; Roy et al.
Conventional self-supporting towers are usually suffi- ciently rigid and a nonlinear analysis is not required. However, flexible towers and guyed structures may require a nonlinear analysis. A guy which becomes slack under certain load cases is an illustration of a geometric nonlinearity.
While this has been done in connection with research projects, such analyses are not presently used in connec- tion with the design of new structures. Slight deviations from these locations will not significantly affect the distribution of forces. The program should also include provisions for automatic handling of planar nodes and mechanisms unstable subas- semblies which will develop in a small group of nodes and members.
Out-of-plane instabilities or mechanisms are generally prevented in actual towers by the bending stiffness of continuous members that pass through the joints. Rossow et al. Nodes 3, 4, 5, and 6 in Fig. The diaphragm in section D- D is a mechanism in the absence of member 8 shown as a dotted line. If two analysts use the same member sizes and assumptions linear, geometrically nonlinear, etc. However, if they use the same assumptions but different member sizes, the corresponding forces may differ.
If the tower was originally designed by manual algebraic or graphical methods and the design loads are not changed, it is quite normal for any computer analysis to indicate forces in the same members which are different from those from the manual methods.
The engineer should determine and document why the differences exist before proceeding with the computer analysis. If the tower is to be upgraded and new design loads specified, then it is normally more cost- effective to rely on a computer analysis. A correlation of past model assumptions with present model assumptions should be performed for the entire structure, not just a part of it.
If moments are anticipated in leg members, it is prudent to use an analysis method that models leg mem- bers as beams. Other members in the tower can still be modeled as truss elements. Latticed masts typically include a very large number of members and are relatively slender, i.
One alternative to modeling a mast as a three-dimensional truss system is to represent it by a model made up of equivalent beams. The proper- ties of an equivalent beam that deflects under shear and moment can be worked out from structural analysis principles.
The beams are con- nected together to form a three-dimensional model of the mast or an entire structure. That model may be analyzed with any three- dimensional finite element program. If large deflections are expected, a second-order geometrically nonlinear analysis should be used Peyrot Once the axial loads, shears, and moments are determined in each equivalent beam, they can be converted into axial loads in the members that make up the beams.
Guidelines for Transmission Line Structural Loading Div, ASCE. Long, L. Power Appar. PAS 1 , Marjerrison, M. Mueller, W. PAS Rossow, E. C, and Chu, S-L. Roy, S. Energy Engr. Zar, M. Gaylord and C. Gaylord, eds. Beck, C. Kempner, L. Lee, J. G, Martin, D. Palmer, A. See Section 9. Where severe vibration is a concern, careful attention must be given to framing details. The practice of blocking the outstanding leg of angles to facilitate the connection should be avoided.
Evaluation of torsional-flexural buckling involves some properties of the cross section which are not encountered in flexural buckling. Proce- dures for computing the torsional constant J, the warping constant C,,, the shear center, and other properties are given in Cold-Formed Steel Design Manual , Timoshenko and Gere , Yu , and other sources.
For cold-formed shapes with small inside-bend radii twice the thick- ness , section properties can be determined on the basis of square cor- ners. Normally, the differences in properties based on square or round corners are not significant. For hot-rolled sections, w is the distance from the edge of the fillet to the extreme fiber, while for cold- formed members it is the distance shown in Fig.
A larger bend radius can be used in fabrication, but for design purposes w should be based on a maximum inside-bend radius of two times the element thickness. Local buckling and purely torsional buckling are identical if the angle has equal legs and is simply supported and free to warp at each end; furthermore, the critical stress for torsional-flexural buckling is only slightly smaller than the critical stress for purely torsional buckling, and for this reason such members have been customarily checked only for flexural and local buckling.
These differ slightly from the corresponding formulas in the first edition of this Manual. The effect of the reduced local-buckling strength on the flexural-buckling strength is accounted for by substituting the reduced value F. Member strengths com- puted by this procedure are in very good agreement with test results on both hot-rolled and cold-formed single angle members Gaylord and Wilhoite These specify K factors which depend upon the connection design for the member.
Curves 1 and 4 in Fig. Curves 2, 3, 5, and 6 are modifications of the basic curves. The effective-length recommendations are based on a review of for- mulas that have been used by the tower industry for many years and are supported by the results of laboratory and full-scale tower tests. Test results on angles with one bolt in one leg and on angles with two bolts in one leg correlate closely with this curve. For reference, the Euler curve with a factor of safety of 1.
A varying K is obtained by comparing the two. A varying K is also obtained by comparing the data in the Bureau of Standards tests with the Euler curve. These relative K values are averaged to provide the values shown in the insert in Fig. The effective lengths prescribed give results that are in very close agreement with numerous tests on both hot-rolled and cold-formed angles Gaylord and Wilhoite The restrained member must be connected to the restraining member with at least two bolts.
An example is shown in Fig. Angle members connected by one leg should have the centroid of the bolt pattern located as close to the centroid of the angle as practicable. Redundant members provide intermediate support for stressed mem- bers.
The magnitude of the load in the redundant member can vary from 0. Ur
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