Page 280 - Design of Reinforced Masonry Structures

CHAPTER 5
COLUMNS

5.1 INTRODUCTION

Vertical members designed to carry axial compression loads, alone or in combinations
with flexure, are called columns. The MSJC Code [5.1] defines column as an isolated
vertical compression member having its horizontal dimension measured at right angles to
its thickness not exceeding 3 times its thickness and having its height greater than 4 times
its thickness (Fig. 5.1). The descriptive “isolated” is not intended to imply that the column
is isolated from other parts of a masonry structure or lateral force resisting system; it is
intended to be used for the application of the MSJC Code provisions for columns as speci-
fied in Code Sections 1.14 and 3.3.4:

1. Minimum side dimension of a column shall be 8 in.
2. The nominal depth of a column shall be not less than 8 in. and not be greater than 3 times
its width.
3. The distance between lateral supports of a column shall not exceed 30 multiplied by its
nominal width.

The above descriptors of a column are usually satisfied in masonry structures. For exam-
ple, an 8-in.-deep (side dimension) reinforced masonry column is not likely to have a width
greater than 24 in. (= 3 × 8), and a height of greater than 60 ft (= 30 × 24 in.) between its
lateral supports (usually top and bottom), and so on. The later requirement is expressed as
h/t limit in examples in this chapter (i.e., h/t ≤ 30).
Vertical loads, in combination with or without flexure, may be also carried by wall
columns that really are parts of a wall which act as columns. When they are fully contained
in the wall, they are called flush wall columns or in-wall columns. Often the wall columns
may project from one or both faces of the wall in which case they are called pilasters

(Fig. 5.2). In addition to carrying vertical loads, pilasters aid in lateral force resistance of
masonry walls of which they are a part. Figure 5.2 shows a typical pilaster projecting only
from one side of the wall.
Reinforced masonry columns can be constructed from either concrete masonry units
(CMU) or bricks (clay masonry) (Fig. 5.3). Both columns and pilasters can be constructed
from standard CMU and bricks, or from special pilaster or chimney units. In both cases,
masonry units should be arranged in running bond so as to avoid continuous head joints.
Masonry columns, like other masonry members, can be designed by either allowable
stress design (ASD) method or the strength method (Fig. 5.4). This chapter presents a dis-
cussion on analysis and design of columns based on strength design philosophy in confor-
mance to MSJC-08 Building Code Requirements for Masonry Structures [5.1], referred to
hereinafter as Code and MSJC-08 Specification for Masonry Structures [5.2], and referred

5.1