CM Exam: Long-span structure

Introduction

This article offers resources for candidates appearing for the chartered membership exam, specifically those with experience in designing long-span roof or frame structures. Examples of such structures include

1. Covered indoor sports centre, community centre, or Leisure Facility
2. Industrial storage facilities or shelters, with or without cranes, also referred to as plant pr process buildings
3. Supermarkets

Two Viable Scheme

Possible configuration of structure can be achieved from the following mindmap

The structure shall be provided with plan bracing and vertical bracing to ensure stability in the longitudinal direction. Alternatively, a portal bay ( refer to Figure 1) is provided for lateral stability.

The main girder/rafter/truss runs along the shorter dimension of the building. Alternatively, one central mega girder/rafter/truss can span along a longer building dimension. This mega truss provides intermediate support to two frames ( inverse L) on either side.

Scheme Development Resources

The design folder to be carried for the exam shall include

1. Sizing of Primary members ( such as main rafter, girder, truss spanning between columns, column), Secondary members ( those spanning between primary members), lateral stability system ( shear wall, braced bay, portal/moment bay, diaphragm, collector, plan bracing), and tertiary members ( such as purlin, roof panel)
2. Calculation procedures with code references, including wind load calculations along the ridge, perpendicular to the ridge (internal pressure coefficient and external pressure coefficients), and local pressure coefficient for panel/girt design.
3. Product Datasheets, including load capacity tables or graphs
4. Rigid frame Member force Calculation ( Steel Designers Manual Kleinlogel Formulas or Frames and Arches Condensed solution for structure by Valerian Leontovich)

Product Datasheets

Insulated Panel

• Tata - Trisomet
• Trimo - Trimoterm
• Kingspan - Quodcore
• Zamil steel
• Tiger Profile
• Hekim Yapi

Single-skin Roof Sheet

• Tata - roofdek
• Steadmans - AS24, AS30, AS35

Z/C (ZED/CEE) Purlin/Girt

• Metsec
• Steadmans (140/170/200/240/300, Sleeved/Butted, Single/Double span)

Rafter/Column

• ArcelorMittal - Cellular Beam
• FabSec FBEAM
• ArcelorMittal - Angelinabeam
• AISC Steel Design Guide 31 - Castellated and Cellular Beam Design
• SCI_P355 Design of Composite Beams with Large Web Openings

Mezzanine Floor System

• Tata Steel Comflor (46,51+,60,80,100,210,225) and Non-composite formwork
• SMD
• Lattice truss Precast Slab ( Omnia Slab / Filigree slab / Hume slab)
• Hollow core slab
• Delta Beam ( Peikko)

Tension Structure System ( Rod/Compression Pin member)

• Macalloy
• Brookforgings
• Leviat - Halfen

Glass

• IStructE publication - Structural use of glass in buildings
• Pilkington

Exam Practise

IStructE UAE Regional group conducts the CM Preparation exam course, which includes a workshop. Candidates share their answer scripts with committee members for feedback. This year (2024) candidates were asked to practise Question 4 from Jan 2024, Private Leisure Facility.

Summary

• The Institute offers sample solutions to past year papers, accessible via the resource search.
• Various videos on the Regional group's YouTube channel offer time management tips, checks, embodied carbon calculation and methods for quick preliminary sizing/analysis for exams.
• The design folder containing information recommended in this article should include load capacity tables, capacity graphs, formulas, and code references.
• For drawings, if the structure is symmetric about one or both axes, draw only half or a quarter of the structure. Ensure sizing of all members ( including approximate reinforcement consumption) for estimation by the QS/planning team. Draw critical connection/joint/construction details between primaries, secondary to primary, facade fixing, foundation, section)
• Geotechnical information should include the safe bearing capacity for shallow foundations and the Elastic modulus (E) for settlement calculations, derived from N Value (Standard Penetration Test) or Cone Penetration Test results. Additionally, calculations for the geotechnical capacity of piles in cohesive, non-cohesive soils, and socketed-in rock for both replacement and displacement piles should be provided, along with details on shoring work and ground improvement techniques.
• Remember, the client may not have a technical background. Emails should provide information that is clear, legible, and positive. Additionally, include a sketch and refer to it in the email for clarity. Mail should help the client to make a decision ahead.
• The recommendation for the final scheme selection should be based on sound criteria, with sustainability considerations included.(Use of score for constructibility, flexibility, sustainability)
• Both Schemes should be viable and should meet client's brief ( Do not change the Client's brief)
• Draw the load path for both gravity and lateral loads until the transfer to the soil. Use the Bending moment diagram, shear force diagram, axial force diagram, and deflected shapes for structural behaviour and Equilibrium ( Sum Fx/Fy/Fz equal to zero)