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Products For Flashings, Accessories, And Reinforcing
1) Flashing For Masonry
2) Masonry Accessories
3) Reinforcing Steel In Masonry
4) Guide Specifications For Masonry Reinforcing
2. Masonry Accessories (continued)
Full size anchor screw detail
Bar positioners
3. Reinforcing Steel In Masonry
3.1. History and Introduction.
Reinforced masonry is a relatively new facet to an old material. Masonry has been used throughout the world since the earliest known history of man. Moses made bricks of clay, the pyramids are stone masonry, the temples in Peru and Central America are stone masonry, and ancient Rome was built of brick. Structures throughout the world have been made of masonry, but only in the last 150 years has reinforced masonry been developed.
Mark Isambard Brunel is credited with the first use of reinforced masonry about 1825 when reinforcing was used with brick in the first major application of a caisson 30 inches thick, 50 feet in diameter and 75 feet deep as part of the Thames tunnel. With the development of portland cement about 1850, concrete and reinforced concrete was developed. The use of portland cement in mortar increased the strength of masonry, which led to its close alliance and identity with concrete.
The development of formulae for the design of reinforced concrete in the middle 1800s was the forerunner to rational design methods for reinforced masonry construction. In 1913 and later in 1919, reinforced brick masonry beams were made and tested to show that this technique does work.
In 1923, British Under Secretary Abe Brebner of India reported on extensive tests conducted on reinforced brick masonry. These tests appeared to be the first organized research on reinforced masonry, and data obtained from them provided answers to questions which had formerly been raised regarding this type of construction. This research in 1923 may be considered as setting the stage for modern development of reinforced masonry. In 1931, in Illinois, two reinforced brick masonry sand storage bins for the Wedron Silica Co. were constructed 25 feet and 16 feet in diameter, both 52 feet high.
A significant impetus was added to the use of reinforced masonry due to the 1933 Long Beach earthquake in Southern California. Prior to 1933, most masonry buildings were unreinforced and constructed with lime mortar. After the earthquake, it was evident that an improved type of masonry would have to be used, and this was reinforced masonry.
Since 1933, major strides have been made in the development of reinforced masonry and its use and adoption in the design and construction of major buildings. At present, reinforced masonry load bearing structures have been built over 22 stories high.
3.2 Function of reinforcing steel. The development of reinforced masonry has a parallel in the development of reinforced concrete. Both systems are heterogeneous, meaning made up of more than one material which have different properties. Masonry, like concrete, is excellent to resist compressive forces but is relatively weak in tension. Steel, on the other hand, is subject to buckling problems when under compression but is excellent when used to resist tension forces. The combination of these two materials, masonry for compression and steel for tension, combine to produce a homogeneous structure capable of resisting great lateral and vertical forces.
Reinforced masonry performs because the materials, steel, masonry, grout and mortar, work together and the temperature coefficient of expansion and contraction for steel, mortar, grout and masonry are very similar. This similarity of thermal coefficients allows all the component materials to act together through all normal temperature ranges, and excessive disruptive stresses are not created at the interface between the steel and the grout to destroy the bond between these materials and thus prevent force transfer.
The reinforcing steel must be locked into the masonry system in such a way as to be capable of being stressed. This mechanism is set up through the grout or mortar. As a beam, retaining wall or building wall is loaded with dead load, live load or lateral loads of earth, seismic or wind forces, it deflects producing compression in the masonry. The forces are transmitted through the masonry, into the grout, through the grout and by bond into the reinforcing steel and thus stressing it in tension.
3.3 Reinforcing Bars.
In the Northwest the majority of reinforcing steel is deformed bars. The deformed bars range from #3 (3/8" diameter), to a recommended maximum of #11 bars (1 3/8" in diameter). This reinforcing steel conforms to ASTM A615-76a, which specifies the physical characteristics of the reinforcing steel. Reinforcing steel may be either Grade 40 with a minimum yield strength of 40,000 psi or Grade 60 with a minimum yield strength of 60,000 psi.
All sizes, #3 through #11, are available in Grade 40 and Grade 60, while the largest size bars, #14 to #18, are available only in Grade 60.
3.3.1. Identification marks. The ASTM specifications cover new billet steel, rail steel and axle steel reinforcing bars (A615, A616, A617 and A706) require identification marks to be rolled into the surface of one side of the bar to denote the producer's mill designation, bar size, type of steel, and for Grade 60 grade marks indicating yield strength. Grade 40 bars show only three marks (no grade mark) in the following order:
1st -- Producing Mill (usually an initial)
2nd -- Bar Size Number (#3 through #18)
3rd -- Type N for New Billet, A for Axle, I for Rail, W for Low Alloy
Grade 60 bars must also show grade marks: 60 or One (1) Line for 60,000 psi strength.
Grade mark lines are smaller and between the two main longitudinal ribs which are on opposite sides of all U.S. made bars. Number grade marks are fourth in order.
| Bar Size | Approximate diameter outside deformations (inches) |
| #3 | 7/16 |
| #4 | 9/16 |
| #5 | 11/16 |
| #6 | 7/8 |
| #7 | 1 |
| #8 | 1-1/8 |
| #9 | 1-1/4 |
| #10 | 1-7/16 |
| #11 | 1-5/8 |
| #14 | 1-7/8 |
| #18 | 2-1/2 |
VARIATIONS: Bar identification marks may also be oriented to read horizontally (at 90 degrees to those illustrated above).
Grade mark lines must be continued at least five deformation spaces.
Grade mark numbers may be placed within separate consecutive deformation spaces to read vertically or horizontally.
3.4. Joint reinforcing. High strength steel wire fabricated in ladder or truss systems are placed in the bed joints to reinforce the wall in the horizontal direction. The most common use of joint reinforcing is to control shrinkage cracking in concrete masonry walls and as part of the minimum steel required by the Uniform Building Code.
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
