Prestressed cable domes: structural behavior and design

Krishnan, Sudarshan

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https://hdl.handle.net/2142/78294 Copy

Description

Title

Prestressed cable domes: structural behavior and design

Author(s)

Krishnan, Sudarshan

Issue Date

2015-01-21

Director of Research (if dissertation) or Advisor (if thesis)

Abrams, Daniel P.

Doctoral Committee Chair(s)

Abrams, Daniel P.

Committee Member(s)

• Gurfinkel, German R.
• LaFave, James M.
• Pecknold, David A.

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• elastic design
• structural behavior
• prestressing
• cable domes

Abstract

The introduction of tension as the predominant means of load transfer offers the potential for using less material to carry more loads. Cable domes are such unconventional structures based on the tensegrity principle. They rely on the assembly of prestressed cables in equilibrium with vertical struts. Members are stressed purely in axial tension or compression and as a consequence, the materials are used efficiently. Not much has been written about the structural design of cable domes. This study was based on an extensive review of technical literature and direct correspondence with the designers of cable domes. The contributions of this study will benefit both structural designers and academic researchers interested in the design of roofs for novel structures such as large arenas and stadia. The primary objective of this dissertation was to provide both an intuitive and mathematical understanding of the structural behavior of radial-type cable domes subject to various loadings, and to determine their limit states. An accompanying objective was to find improved methods for their design and construction. To accomplish these goals, a series of twelve 400 ft. span domes with varying depth-to-span ratios, number of polygon sides and number of polygonal hoops were examined. Three limit states were evaluated, namely 1) buckling of struts, 2) serviceability, and 3) rupture of cables. The main cause of instability was established and a potential design solution in the form of enhanced struts has been recommended. The study was made efficient by the use of a two-dimensional model. For dome designs governed by axisymmetric loads, the planar model was sufficient for member design. The analysis procedure was further streamlined using an influence surface analysis (based on the Müller-Breslau principle) that helped to identify governing load combinations for the design of members. Domes vulnerable to wind uplift were recognized and prestressing force levels were increased accordingly. As such, the findings from the influence surface analysis proved to be a good indicator of the adequacy of prestressing forces assigned to a dome. Further, the results revealed that additional prestressing forces were necessary to meet the serviceability criterion, beyond simply ensuring that cables remained in tension under all loading conditions. The most important geometric parameters for structural design were identified as: the number of sectors, the number of polygonal hoops, hoop radii, rise-to-span ratio, and depth-to-span ratio. They greatly influenced the amount of prestressing forces required for the overall stability of a dome. The results showed that the radial stiffness of a hoop cable is inversely proportional to the hoop radii and the number of sectors. Domes with smaller depth-to-span ratios required higher prestressing forces for stability and to achieve a desired elevation (shape). The critical loads for strut members were determined using the Stiffness-Probe Method. The method gave a physical understanding of the loss of capacity in struts due to applied axial loading. The use of prestressed stays increased a strut’s buckling capacity to more than four times when compared with the critical loads of struts without stays. Consequently, stayed-struts are recommended as an alternative design solution for enhancing the load-carrying capacity of cable domes. The erection procedure for cable domes typically constitutes 40% of the project cost. Noting that the strut forces were relatively small when compared with the diagonal cable forces, prestressing the struts as part of the erection process may prove to be an economical alternative for reducing the overall project cost. This approach has been proposed for future study. For well-designed cable domes, i.e., domes that are adequately prestressed and whose cables remain in tension under all loading conditions, the study revealed that the cause for potential dome demise is usually due to buckling of struts or displacements exceeding the acceptable ranges for serviceability. As these limit states were found to occur well within the elastic range of the members, the findings justify the use of elastic design for cable domes.

Graduation Semester

2015-5

Type of Resource

text

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http://hdl.handle.net/2142/78294

Copyright and License Information

Copyright 2015 Sudarshan Krishnan

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