Civil Engineering Association

Dear members,

Please someone upload the following papers:

Limit states design of antenna towers

Authors:
Yohanna M. F. Wahba, Murty K. S. Madugula, Gerard R. Monforton

ABSTRACT:
The Canadian Standard CAN/CSA-S37-M86 “Antennas, towers and antenna supporting structures” follows a quasi-limit states approach in which the member forces determined for specified loads are multiplied by a unified factor and compared with factored resistances given in CAN3-S16.1-M84. This results in designs basically the same as those resulting from a working stress design with a factor of safety of 5/3. Such structures exhibit a non-linear structural behaviour even under service loads. Thus the effect of ice accretion and direct interaction between wind and ice does not permit the load factors specified in CAN/CSA-S16.1-M89 “Limit states design of steel structures” to be directly applied to antenna supporting structures.In this study, 41 different towers (representing various heights and designed for different ice classes and wind pressures) were analyzed under specified loads and then under a set of factored loads. From the comparison of the design forces in the towers with those calculated according to the existing standard, a set of partial load factors was derived. The new load factors to be used in the 1993 edition of S37 are presented and justified. Key words: antenna towers, guyed towers, ice and wind loads, limit states design, self-supporting towers, working stress design.

Effect of guy initial tension on design of guyed antenna towers

Authors:
Yohanna M. F. Wahba, Murty K. S. Madugula, Gerard R. Monforton

ABSTRACT:
This study examines the effect of changing the initial guy tension on the design of guyed antenna towers. Six different guyed towers with various heights and loading conditions are used in this study, in which initial guy tensions are changed and the corresponding effect on the forces in the tower components are examined. Also, the methods used in measuring the initial tension are reviewed. On the basis of this study, it is proposed that the initial guy tensions have a load factor different from the value of 1.0 suggested in CSA S37-94. Two additional load combinations are developed from this analysis in order to assist design engineers in determining the worst case scenario for the variation of initial tension in the guys. Results are compared for designs using the current design procedures and the design using the proposed load factors for initial tensions in guy wires. Key words: antenna towers, guyed towers, limit states design, guys, initial tension.


regards,
apocalipse

Dear members,

Please someone upload the following papers:

Buckling of built-up compression members in the plane of the connector


Authors:
Murray C. Temple, Ghada Elmahdy

ABSTRACT:
An examination of the requirements for the design of built-up compression members in the North American and European standards and specifications reveals a great variation in the allowable maximum slenderness ratio for an individual main member, and also in the determination of an equivalent slenderness ratio. The requirements of the Canadian standard with regard to the determination of the maximum allowable slenderness ratio of a main member between points of connection can be a bit confusing.This research involved a study of model built-up members that buckled about an axis perpendicular to the plane of the connectors. Twenty-four tests were conducted on model built-up members. The theoretical analysis consisted of a finite element analysis of the model built-up struts. In addition, an equivalent slenderness ratio was calculated by several methods. These equivalent slenderness ratios were then used in conjunction with the requirements of the Canadian standard to calculate a compressive resistance, which was compared with the experimental failure load.From this research on built-up members that buckle about an axis perpendicular to the plane of the connectors it was found that at least two connectors should be used, that the slenderness ratio of the main member between points of connection has a significant effect on the compressive resistance, and that Timoshenko's equivalent slenderness ratio when used in conjunction with the Canadian standard gives results that are in the best agreement with the experimental results.


Equivalent slenderness ratio for built-up members

Authors:
Murray C. Temple, Ghada Elmahdy

ABSTRACT
Built-up struts that buckle about an axis perpendicular to the plane of the connectors should be treated as a "built-up" member as opposed to a "simple" member. This mode of buckling causes shear and moments in the connectors which deform the connectors. These deformations increase the lateral deformation of the member and hence affect the load-carrying capacity. To account for this effect the easiest method is to use an equivalent slenderness ratio such as the one included in the Canadian Standard. This note outlines the derivation of the equivalent slenderness ratio equation, discusses when it should and should not be used, and includes a numerical example. A rewording of the applicable clause in the Canadian Standard is suggested.



Slenderness ratio of main members between interconnectors of built-up compression member

Authors:
Murray C. Temple, Ghada M. Elmahdy

ABSTRACT
Many steel design standards, including CAN/CSA-S16.1-M89 "Limit states design of steel structures," specify maximum slenderness ratios for the individual main members between the interconnectors of built-up compression members. Previous research on which these requirements are based is reviewed. It is shown that the imperfection sensitivity due to coupled instabilities is measured from bifurcation critical loads. However, steel standards are based on a compressive resistance determined for a member with an initial out-of-straightness and a suitable residual stress pattern. It is shown that the use of an equivalent slenderness ratio equation is sufficient to predict the compressive resistance of these built-up members. Further restrictions on the slenderness ratio of built-up members between interconnectors are not warranted. Thus, the elimination of these requirements from S16.1-94 is justified. Key words: built-up members, codes, compressive resistance, coupled instabilities, equivalent slenderness ratio, interconnectors.


regards,
apocalipse