Civil Engineering Reference
In-Depth Information
Chapter 20
Masonry
Andrew Rolf
Senior Engineer, Arup, UK
doi: 10.1680/mosd.41448.0369
CONTENTS
20.1
Introduction
369
20.2
System selection
369
20.3
Preliminary sizing
376
This chapter introduces masonry construction and its components. It provides background
information on the basic concepts of masonry construction, covering load-bearing and non-
load-bearing construction techniques. This chapter also provides details of the masonry units
available and widely used in the UK; typical jointing and bonding techniques; and restraint
systems often employed in masonry construction. The chapter gives some rules of thumb
for initial sizing of various forms of construction to aid with preliminary/initial design.
Introductory information is provided on the design of masonry under seismic conditions, and
the principles outlined in the Eurocodes. The chapter presents some detailed design examples
on masonry under local, vertical and lateral loads.
20.4
Seismic design
382
20.5
Final design
382
20.6
References
396
20.1 Introduction
Masonry is the generic term used to describe the matrix of clay,
concrete, stone or calcium silicate units (bricks or blocks) with
cement or lime based mortars. Masonry construction is widely
used throughout Europe and extensively used in the construc-
tion of low to medium rise buildings within the UK.
Masonry is often used in load-bearing construction, clad-
ding to frame buildings or for isolated structures such as free-
standing or retaining walls. The choice of construction will
often depend on a number of factors, such as:
Type of space, i.e. residential, office■■
consistent spacing of walls or avoidance of short walls
■
or piers;
limitation of large spans onto masonry units;
■
avoidance of large openings.
■
Modern load-bearing masonry construction is often limited to
buildings less than three storeys or 12 m. Above this height
load-bearing masonry construction can begin to become
uneconomical.
20.2.1.2 Cladding
For larger buildings where future flexibility is critical or where
large spans required, masonry is often employed as cladding.
Cavity construction is the norm, with inner and outer leaves of
masonry or an outer leaf of masonry supported by lightweight
steel or timber studwork inner leaf.
Masonry used as cladding is still load-bearing as it sup-
ports lateral (wind) and vertical (self-weight) loads. This is
important, as rules on slenderness and allowable panel size
will still apply.
For framed buildings, such as offices, masonry can be con-
structed in panel sizes in excess of those normal for load-
bearing masonry; i.e. 4 m high and 6 m wide. This will result
in the need for secondary support elements such as wind posts
or head/cill beams.
Masonry cladding is often supported on shelf angles fixed to
slab edges. Typically these can sustain 10-14 kN/m, meaning
two storeys of masonry. BS 5628 (clause 25.3.2) suggested a
limitation of 9 m height or three storeys for support to the outer
leaf in these situations.
The detailing of masonry cladding is critical to ensure satis-
factory performance. This includes the location of movement
joints (horizontal and vertical), restraints, location of support
angles and location of secondary supports (wind posts, etc.).
■
Geometry, i.e. clear span or cellular
■
Acoustic separation, i.e. acoustic partitioning or floors■■
■
Fire resistance
■
Flexibility of spaces
■
Aesthetics.
■
20.2 System selection
20.2.1 Forms of construction
20.2.1.1 Load-bearing masonry
Load-bearing masonry is suited to cellular low rise building
forms in modern construction, with much of the domestic con-
struction in Europe being load-bearing masonry. For larger
buildings masonry is often specified as a cladding material for
aesthetic reasons.
Historically load-bearing masonry has been used for larger
building forms (over five storeys). However, these forms of
construction are now often unfeasible given the large volume
of structure used to create the load-bearing elements.
To utilise load-bearing construction effectively, mitigat-
ing complicated detailing or excessive use of ancillary prod-
ucts (wind posts, etc.), buildings should have the following
features:
cellular in plan with consistent cross walls to form stability;
20.2.1.3 Retaining and free-standing walls
Free-standing walls typically need only support self-weight
and lateral loads. These are designed as cantilever elements
■
limited floor to ceiling heights (ideally less than 3 m);
■
