Masonry Magazine September 1976 Page. 20
3)
By the basic economy of reinforced masonry which is fireproof, compared to steel which must be protected by concrete or plaster to be fireproof.
4)
By the energy conservation in the combination of masonry with limited glass that together reduce the cost of building utility operations.
New Concept
The concept of 8 inch thick concrete block walls holding up a building 12 stories high or even higher is quite an innovation that isn't easy to comprehend. As a comparison, the Swiss, who have been pioneers in load-bearing bearing masonry construction, have built apartments with 15¼" thick outside walls to heights of 18 stories (way back in 1957).
In "modern masonry" the structural frame is eliminated completely and all structural loads are carried by the re-inforced concrete block or brick masonry bearing walls and precast or cast-in-place concrete slabs. The masonry stiffens the steel and protects it from fire, while the steel adds resilience and toughness to the wall.
In concrete block construction, vertical steel is placed inside certain hollow cells of hi-stress concrete block and these cells are then filled with a rich soupy grout mixture of cement, sand and pea gravel. Horizontal steel is grouted in bond beams, which are masonry units depressed on the top to form a horizontal channel in the wall.
In areas of the country outside major seismic or earth-quake zones, where wind loads govern design, the only difference in application would be to install steel of smaller diameter, further apart within cells of standard block to achieve the same structural results as we get in California or Hawaii. Comparative costs also are less, due to lower labor factors and less reinforcing. This use of modern masonry has expanded rapidly since the first application in multi-story buildings by Hendrick and Mock. There are two main reasons for this popularity; the first being economy. The Hanalei was built at a cost of $11.44 per square foot including elevators and 4-pipe air conditioning. This proved to be 20% less than similar projects employing other types of construction.
In recent projects the total cost per square foot has risen, due mainly to higher labor and material costs, but the relative economies remain. Even with overtime work authorized in the early stages of construction of the 10-story Town & Country Hotel Addition, and an expensive foundation using clusters of 60 ft. long piles, the cost was only $16.30 per square foot. This was about equal to the cost of the average custom built home in California and far less than other Class A Structures. The Convention Center Ramada Inn 12-story hotel tower which was completed in 1972 in Dallas, Texas cost $14.73 per square foot. This cost included a complete restaurant and meeting room complex on the top floor. For total project preliminary design budgets we are currently using 24 to 26 dollars/square foot in California and 22 to 24 dollars/square foot in the south-west (Texas). East coast costs should run close to California and the mid-west should be slightly higher than the southwest.
The second reason is savings in construction time. The erection time for all walls, floors and the roof of the 207 room Hanalei, was 8 weeks. The total construction time from the start on February 11th, until the hotel was ready for occupancy four months later, was 141 days. The 324 room Town & Country Hotel which was completed in stages, took 208 total days for all work, not quite 7 months. Floor and roof slabs for both projects were job cast on the ground and lifted into place by use of a truck crane.
In Texas we have been achieving similar results using flying forms since large truck cranes capable of lifting floor slabs that could weigh from 9 to 14 tons are not as available as climbing tower cranes and our sites have been quite tight. Construction of the 12-story Ramada Inn Convention Center Hotel in Dallas, was commenced on June 4, 1971. The hotel was substantially complete and opened for business on June 19, 1972. Masonry work began in October, 1971 and was complete on February 9, 1972. Total time for masonry work on the 12-story, 162,000 square foot hotel tower was just 64 working days! (18 days were lost to bad weather and holidays).
To illustrate what an early opening means to a Owner, just consider the revenue produced by the advance opening of the 194 room center wing of the 324 room Town and Country in 148 days. The wing had a 100% occupancy during high tourist season from July 4th, until the 60 room east wing opened August 15th (after 194 days), and the 70 room west wing was opened August 29th. (after 208 days). This created 10,864 room day rentals at $19.40 average per occupied room which is equal to $215,107.00 or about $40,000 plus gross profit. Obviously the 100% rental only occurs in the summer tourist season, but even maintaining occupancy on a 70% average for this period certainly wouldn't be hard to take.
About The Author
John R. Mock, President, Hendrick & Mock Architects, San Diego, Calif, is one of North America's leading authorities on loadbearing masonry structures. His firm has designed many out. standing loadbearing structures in recent years and has several more in the planning stage. Many will remember him for his excellent presentation at the 76 MCAA Convention held at the Town & Country Hotel. San Diego.
Introduction To Case Studies
Although the case studies to be presented are constructed in Hawaii, California and Texas, the buildings actually represent enough variations to indicate what to expect of the system in any region of the country. All major building code requirements are quite similar regarding this type of construction.
First of all, California and Hawaii are located in earth-quake country. This state and Hawaii and the other western states, to a lesser degree, represent the most-restrictive structural requirements possible. This area also maintains a very high construction cost index. However, labor is quote productive and contractors are quite competitive. They also are receptive to new systems. Hawaii is a special problem unto itself, but the relative cost savings still exist.
The Dallas-Fort Worth and Austin, Texas regions are representative of the growing south and southwestern parts of the country. Physically these areas look much like the mid-west and certain areas of the east.
Buildings must be designed for extreme temperature differences and rainfall is substantial. It is relatively hot much of the year but snow and freezing also occur during the winter months. Actually a building designed for these parts of Texas could be relocated in any one of the more severe hot or cold weather climates of the country with few changes.
As with any area, most buildings and their Owner's requirements are also different.
With this, or any other building system, a little common sense goes a long way. Therefore, the information presented in the case studies should service as a starting point for designing and construction of this system.
masonry September, 1976