anchors for shoring systems

68 Pages·2016·3.78 MB·English

by  Suzanne Wilson

SHIRLEY CONSULTING ENGINEERS
PTY LTD
INVESTIGATIVE, REMEDIAL & GROUND ENGINEERING
ANCHOR DESIGN & CONSTRUCTION
FOR SHORING SYSTEMS
FUNDAMENTALS and AS4678
Civil & Structural Engineering Panel
19 March 2013
Andrew Shirley & Simon Fagg
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
INTRODUCTION - 1
1. Soil & Ground Anchors for Shoring Systems.
2. Failures due to limited understanding &
reliance on ‘expert contractors’.
3. Some engineers are simplistic in their anchor
specifications, and just ‘call up the load
required’.
4. Become litigation ‘targets’ when the anchor /
shoring system fails.
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
INTRODUCTION
This Presentation will cover:
1. The Fundamentals of Anchor Design for Shoring
Systems.
2. The differences between soil anchors & anchors and
usual reasons why anchors & shoring systems fail.
3. The requirements of AS 4678 and its implications for
design engineers.
4. Five case studies of failures because the Design
Fundamentals have not been followed.
5. Lessons for Design Purposes.
6. The Risks & Liability Issues for Engineers
7. A pdf version of the PowerPoint Slides will be available
on our website www.shirley.net.au
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
EXAMPLE OF TYPICAL ANCHOR SPEC.
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
EXAMPLE OF TYPICAL ANCHOR SPEC.
A correct understanding of the way in which the anchors
interact with the structural shoring system [viz: soil /
structure interaction] is essential.
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
ANCHORS FOR SHORING SYSTEMS
1. Anchors are NOT the same.
2. Many types of anchor; each type of anchor
interacts differently with the structural part of
the shoring.
3. Only limited information on the design of
shoring wall anchors is generally available [e.g.
CIRIA C580].
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
ANCHORS FOR SHORING SYSTEMS
Anchors fall into three Categories
Rock Anchors Soil Anchors Dead Man Anchors
• Stiff Anchorage • Deformable Anchorage • Shallow Anchorage
• No load transferred from • Anchorage Zone • Surficial Failure of Dead
the Rock to the Soil Interacts with the Man, typically not within
Restrained Zone the Restrained Zone
• No interaction between
Anchorage Zone and • Where problems are • Minimal interaction
Restrained Zone most frequent, and topic between
of this talk Anchorage Zone and
Restrained Zone
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
ANCHORS WITH AN ANCHORAGE IN ROCK
Anchorages in rock are very common & rarely fail
unless they are too short. Why?
1. Rock anchors are ‘stiff’ elements.
2. Rock Anchors form Structural Frame
with the rock and structural parts.
3. Rock Anchors have a Large Overload
Capacity.
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
SOIL ANCHORS vs ROCK ANCHORS
• Anchors into
rock form a
‘Frame’
• Soil Anchors do
NOT create a
‘Frame’. Only a
Restrained
Cantilever
• Soil Anchor
MUST be able to
‘self tension’
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au
ANCHORS WITH AN ANCHORAGE IN SOIL
Why do Soil Anchors Fail?
1. No Structural Frame.
2. Minimal / No Overload Capacity.
3. Incorrect Lock-Off Load.
4. Unable to ‘self tension’ if installed
at too steep an angle.
© Shirley Consulting Engineers Pty Ltd www.shirley.net.au