2005 MSJC Masonry Code and
Specification Changes
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Changes
Ten of the Top Changes
by Richard E. Klingner and Jason J. Thompson, respectively, Chair
and Secretary, MSJC
The Masonry Standards Joint Committee (MSJC) develops the Building
Code Requirements for Masonry Structures (ACI 530/ASCE 5/TMS
402) and Specification for Masonry Structures (ACI 530.1/ASCE
6/TMS 602), plus corresponding commentaries. These ANSI-consensus
documents govern the structural design of new masonry in the U.S.
The latest edition of these documents, the 2005 MSJC Code and
Specification, is now available from The Masonry Society (TMS),
the American Concrete Institute (ACI), and the American Society
of Civil Engineers (ASCE). It is expected to be adopted by reference
by model codes. The purpose of this article is to give readers an
overview of what's new for the 2005 edition, with particular attention
to changes that are expected to affect material suppliers. Code
sections and Specification articles listed are based on
the 2005 edition.
The 2005 edition contains more than 500 updates and improvements
over the 2002 edition. The 2005 edition is easier to use, particularly
for those accustomed to reinforced concrete design. The Specification
is considered by reference to be part of the Code.
Here is a list of significant updates and revisions:
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| AAC is a cement-based material that contains
a large volume of voids, making it so light that it floats.
This unique product has numerous benefits that suit it to construction,
including excellent insulating properties, ease of working and
handling, and fire resistance. |
1) Autoclaved aerated concrete (AAC) masonry has been added to
the Code (Appendix A) and Specification. Design
provisions are similar to those of Chapter 3 (Strength Design),
and design examples will be included in the 5th Edition of the Masonry
Designers' Guide, scheduled for publication later this year
by TMS with support from the Council for Masonry Research. This
innovative product has many useful structural, thermal, and acoustical
characteristics, and also has excellent passive fire resistance.
It is expected to offer many new opportunities for the increased
use of cementitious materials.
2) Maximum reinforcement limits have been revised for strength
design (Section 3.3.3.5). The limits of the 2002 edition have been
modified based on performance requirements that are related directly
to expected seismic ductility demands. In addition, instead of limiting
maximum reinforcement, a designer can also use confined “special”boundary
elements, whose design and detailing requirements must be determined
by test.
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| Testing on wall panels demonstrates the feasibility
of high-lift grouting |
3) The maximum height for a grout lift (increment of grout height
placed within a total grout pour) has been increased from 5 ft to
12.67 ft (1.52 m to 3.86 m), under carefully controlled conditions
that include a minimum curing duration of 4 hours, a consistent
grout slump between 10 in. and 11 in. (254 mm and 279 mm), and the
absence of reinforced bond beams between the top and the bottom
of the grout pour (Article 3.5 D). This is expected to promote significant
increases in contractor productivity, particularly for large, box-type
buildings.
4) New prescriptive requirements have been introduced for anchored
veneer in geographic areas with basic wind speeds between 110 mph
and 130 mph (Section 6.2.2.11). Essentially, current provisions
have been extended, with requirements for closer spacing of anchors
to resist the higher design wind loads. This will encourage the
use of veneer in wider geographic regions of the U.S., and will
make its design more cost effective.
5) Allowable stress and strength-design provisions for lap splices
and development lengths have been harmonized. The strength-reduction
factor has been removed from strength-design provisions (different
calibration), and the barsize factor has been slightly modified
(Sections 2.1.10 and 3.3.3). Active work in this area is expected
to continue over the next several years.
6) In contrast to previous editions of the Code, in-plane
allowable flexural tension is no longer zero (Section 2.2.3.2),
but has the same value as for out-of-plane flexural tension. This
common-sense change will make the design of unreinforced masonry
shear walls easier, and also harmonize allowable stress and strength
design. In a related update, the modulus of rupture has been harmonized
in strength design (Section 3.1.8.2), so that its value is now the
same for in-plane bending and out-of-plane bending. These changes
are expected to make the 2005 edition easier for designers to understand
and use.
7) To avoid potential issues with OSHA requirements for control
of silica dust, wet-cutting of CMU is explicitly permitted (Article
3.2 C). This clarification is expected to have very positive implications
for material suppliers. Masonry units must often be cut at the job
site, and control of the resulting silica dust, while necessary
from a health standpoint, can also be expensive. By far the most
cost-effective way to control silica dust is by wet-cutting units.
Previous editions of the Specification, which prohibited
wetting concrete masonry units, had been interpreted by some as
prohibiting wet-cutting. This clarification will let masonry continue
to be constructed in a costeffective manner.
8) Design provisions for prestressed masonry, formerly based on
allowable stress design with strength checks, are now based on strength
design with serviceability checks, and are also updated in many
other ways (Chapter 4). These updates are intended to make the provisions
more friendly to those accustomed to strength design of prestressed
concrete. This is expected to encourage the use of prestressed masonry.
9) Empirical design provisions have been updated so that they will
continue to be available for appropriate use. They are now limited
based upon element height and elevation, as well as geographic location
(Section 5.1.2.3). This change is intended to avoid potentially
unsafe situations, such as the empirical design of a penthouse on
top of a 100-story building. Provisions have been clarified to require
that axial gravity loads must act within the kern (that is, the
center third) of an element's cross-section (Section 5.1.2.1).
10) Additional Code requirements have been moved from
the chapters dealing with different design approaches, to the front
of the Code. These include corbel design, which has been
moved from Chapter 5 (Empirical Design) to Section 1.12 (General
Requirements), so that prescriptive requirements for corbels are
independent of how they are designed.
The ten changes detailed here are just a few of the many revisions
made in this code cycle. Several other important changes have improved
the clarity, organization, and utility of the Code and Specification.
During the present 2008 code cycle, the MSJC will continue to strive,
within an ANSI-accredited framework, for technically sound provisions
that protect public welfare and create a level playing field on
which masonry can compete fairly with other materials. MSJC meetings
are open to the public. If you would like more information about
the MSJC, see www.masonrystandards.org
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