Civil Engineering Reference
In-Depth Information
CHAPTER 4
Retrofitting Design of Masonry Structures
4.1
Introduction
Masonry is a kind of load-bearing material made of the block materials (bricks or masonry
blocks) bonded together by mortar. Compared with concrete, masonry has a certain ca-
pacity of compressive strength but lower capacity in tensile, shearing and bending strength.
Therefore, masonry structure especially plain masonry has a very poor integrity, rather low
capacity of load-bearing and is vulnerable to crack under external loads. Masonry needs to
be repaired and retrofitted in the following situations:
a. Settlement cracks were formed in the wall because of the uneven settlement of founda-
tion.
b. Temperature cracks were engendered in the wall because of thermal expansion and
contraction of roof.
c. Bearing capacity was insucient in local masonry walls and columns.
d. Deficiency of bearing capacity in original masonry structure caused by adding stories
or rebuilding.
e. Seismic strength is insucient or unsatisfactory and seismic constructional measures of
the building are not satisfactory according to the earthquake resistant evaluation in seismic
protection area.
f. Building damaged after earthquake.
Retrofitting methods in common use for masonry structures include the methods of direct
retrofitting, changing load transferring path and adding outside structure.
Direct retrofitting method refers to retrofitting or repairing the structural member whose
strength is insucient and constructional measures cannot meet the demand, without chang-
ing load-bearing system and plan layout.
The method of changing load transferring path means changing plan layout and load trans-
ferring path. It usually necessitates adding bearing walls, columns, and their corresponding
foundations.
The method of adding outside structure means adding concrete or steel structure outside
the original structure to transfer partial loads of original structure and loads of extension
story structure directly to the foundation through outside structure. It is mainly used in
the construction of additional stories.
This chapter mainly introduces several usual direct retrofitting methods for multi-story
masonry brick buildings. The retrofitting design of multi-story block masonry buildings,
inner-frame masonry buildings and frame supported masonry buildings are covered in Chap-
ters 3 and 4.
4.2
Repairing and Strengthening of Wall Cracks
Wall cracks appear when uneven settlement, thermal expansion and cold shrinkage, lack
of bearing capacity and earthquake occur. Repairing and strengthening may be used for
crack retrofitting when crack expansion stops.
a. Grouting can be used in large walls with few cracks.
