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Hanns U. Baumann

As a consulting structural engineer in Southern California since1961, Hanns U. Baumann has been personally involved in the development of more than 30 new construction products, mainly relating to reinforced concrete construction. An inventor of construction products himself, he has been granted 7 U.S. patents and is named as co-inventor on 2 additional patents. Beginning in 1960, his Gascon fiber reinforced lightweight polymer concrete system has been used to construct homes in 10 countries. As co-founder of Conspray Construction System, Inc. in 1970, he has pioneered the development of wet shotcrete technology. In 1992 he won the Construction Innovation Forum's Nova Award for his invention of the BauGrid® Construction System (B/GCS). Baumann Research and Development Corp., founded by Baumann, has been developing his inventions since 1986. BauTech, Inc. is currently marketing his inventions under exclusive license, and is in the process of negotiating with several prospective licensees in the country of Japan. B/GCS was a finalist for the 1996 Civil Engineering Research Foundation (CERF) Charles Pankow Award presented by the American Society of Civil Engineers. Baumann has served on the Board of Directors of the Construction Innovation Forum (CIF) and the Corporate Advisory Board of the Civil Engineering Research Foundation, and is Chairman of ACI 439G Reinforcing Steel Committee, Welded Reinforcement Grids Subcommittee, and has served on the Strategic Development Council of ACI International. He was the Keynote Speaker at CIF’s 1998 Annual Awards banquet, and was a featured speaker at the SEWC in Brazil in 199?.

Hanns can be reached at (949) 361-0888 or hanns@brdcorp.com

1) R. Park and T. Pauly, “Reinforced Concrete Structures”, University of Canterbury, Christchurch, New Zealand, August 1974 2) F.E. Richart, A Brandtzaeg, and R.L. Brown, “A Study of the Failure of Concrete Under Combined Compressive Stresses,” University of Illinois Engineering Experimental Station, Bulletin No.185, 1928, 104 pp.

1) F.E. Richart, A Brandtzaeg, and R.L. Brown, “A Study of the Failure of Concrete Under Combined Compressive Stresses,” University of Illinois Engineering Experimental Station, Bulletin No.185, 1928, 104 pp. 2) “For each curve the fluid pressure was held constant while the axial compressive stress was increased to failure and the axial strains measured. The tests were carried out over short-term periods. It is evident that an increase in lateral pressure brings very significant increase in the ductility as well as strength. This effect is due to the lateral pressure that confines the concrete and receives the tendency for internal cracking and volume increase just prior to failure.“

1) R. Park and T. Pauly, “Reinforced Concrete Structures”, University of Canterbury, Christchurch, New Zealand, August 1974

N. M. Newmark and W. J. Hall, “Earthquake Resistant Design”, McGraw Hill Inc., 1979

Labor Intensive

Dimensional Problems of Conventional Reinforcement

Present-Day Codes

Because of the limitations of the machines used in present-day technology to fabricate conventional reinforcing steel, codes still allow a large dimensional tolerance of ± 13mm (± ½).

Bar Confinement Problems

When conventional hoops are installed as shown, the hoops do not confine the longitudinal rebar when it is resisting axial compressive forces, Consequently in past earthquakes these unconfined rebars have buckled causing failures.

Conventional hoop and crosstie transverse reinforcement has caused many constructability problems for design and construction engineers since the importance of ductility was first recognized. Hoop and crosstie reinforcement is fabricated on benders, to very loose dimensional tolerance of ±13 mm (± 1/2"). Poor fitting hoops caused damage in structures during the Loma Prieta earthquake, as shown in the above photo.

Another very significant problem with the use of crosstie reinforcement with 90° hooks embedded in the concrete cover, is that during a violent earthquake the concrete cover is lost due to spalling. Premature crosstie failure in laboratory experiments by Professor Shamin Sheik are shown in this figure. Based on this evidence, engineers on seismic code writing committees now require seismic hooks at both ends of crossties and should also prohibit 90° hooks in concrete cover.

Another major cause of the re-occurring constructability problems, is the many layers of closely spaced hoops and crossties which inhibit the flow of concrete during placement. Also, the many seismic hooks not only impede the concrete flow but also obstruct the movement of the vibrating compactor.

Welded Reinforcement Grids (WRG) is the generic name for the proprietary BauGrid® Reinforcement System (B/GRS) products that are commercially available through BauTech, Inc. of San Clemente, California, U.S.A.

Starting in 1987, a solution to the constructability problem plaguing conventional transverse reinforcement has been under development. Tested in laboratories at five U.S. universities and the national laboratories of Canada and the U.S., Welded Reinforcement Grids (WRG) have solved constructability problems. Members reinforced with WRG have shown ductile performance superior to those with conventional transverse reinforcement. Professor Murat Saatcioglu attributes this superior ductile performance to the welds at each intersecting rod of the WRG which creates many smaller confinement cells inside the structural member. The WRG are manufactured under a very strict quality assurance program, approved and monitored by the International Council of Building Officials (ICBO), which in 1999 issued an Evaluation Report ER-5192. Similar approvals have been issued by the cities of Los Angeles, San Francisco, San Diego, Phoenix and New York.

The advantages of BauGrid® are,

1. Elimination of rebar congestion. One BauGrid® replaces many pieces of traditional reinforcement. 2. BauGrids® allow for more rapid cage assembly and installation, using less labor. Because of the ±1/8" dimensional accuracy, BauGrids® are ideal for rapid off-site cage assembly.

3. BauGrids® allow for more rapid concrete placement, using less labor.

4. BauGrids® allow for more rapid form installation, using less labor.

5. BauGrids® improve seismic resistance with greater and more reliable ductile performance.

6. BauGrids® provide more accurate rebar placement.

7. BauGrids® provide higher strength than traditional reinforcement

8. BauGrids® improve the ductility performance of high performance concrete

A 42-story building in San Francisco has more than 500 tons of 2.4m x 2.4m (8'x8') L-shaped and T-shaped BauGrids® specified in 61 cm (24") thick concrete elevator-core boundary shearwalls. The contractor, Webcor, reports labor saving in assembly and installation similar to those reported by the contractor in San Diego. The BauGrids® with 16mm (5/8") diameter welded rods are shipped very efficiently on pallets to the BauCage assembly plant. There, BauCages are rapidly assembled with very few workers, because one BauGrid® can replace up to 32 separate pieces of conventional reinforcement.

A 24-story building constructed in San Diego California, U.S.A utilized a proprietary product developed by BauTech to speed construction of heavily reinforced concrete bearing /shearwalls around the elevator core. BauCages two-stories high by up to 3.7m wide are installed and then quickly connected on their common vertical edges by insertion of BauSplicegrids™ and then the charging of vertical locking bars. The contractor reported a 50% labor reduction in cage assembly and 40% labor reduction in cage installation.

The BauLinkbeam™ is a new proprietary BauTech product for use as coupler beams in shearwalls. Because BauGrids® are manufactured to very exact dimensional tolerance ±3mm(±1/8"), BauCages with BauLinkbeam™ can be fabricated so that when BauCages are quickly assembled on-site, the whole element has a dimensional accuracy of ±6mm (±1/4"). The BauLinkbeam™ horizontal and diagonal bars can then be rapidly charged without hitting the vertical boundary element bars.

Following are some of the research papers describing the superior performance of BauGrids®. 1. Saatcioglu, M., and Grira, M., 1999, "Confinement of Reinforced Concrete Columns with Welded Reinforcement Grids," ACI Structural Journal, V.96, No. 1, Jan-Feb., pp29-39. 2. Saatcioglu, M., and Grira, M., 1997, "Material Tests for Welded Reinforcement Grids", Report OCEERC97-17, University of Ottawa. 3. Saatcioglu, M., and Grira, M., 1996, "Concrete Columns Confined with Welded Reinforcement Grids", Report OCEERC96-05, University of Ottawa. 4. Cheok, Gerldine S., and Stone, Willaim C., 1994, "Performance of 1/3-Scale Model Precast Concrete Beam-Column Connections Subjected to Cyclic Inelastic Loads - Report No. 4", Building and Fire Research Laboratory, Report, National Institute of Standards and Technology. 5. Baumann, H. 1992, "Performance of Prefabricated High Strength Welded Wire Grids in Ductile Concrete Shearwall Boundary Elements", The International Journal of The Structural Design of Tall Building, First Issue Autumn 1992. 6. Miranda, Eduardo, and Thompson, Christopher L., and Bertero, Vitelmo V., 1990, "Cyclic Behavior of Shear Wall Boundary Elements Incorporating Prefabricated Welded Wire Hoops". Report, Earthquake Engineering Research Center, University of California at Berkeley.

Starting in 1993, BauTech, Inc. has been a development team member on the PRESSS Hybrid System Development Project. The PRESSS Program has been sponsored mainly by Mr. Charles Pankow and Charles Pankow Builders, Ltd,, with partial funding by the National Science Foundation (NSF) and the Precast/Prestressed Institute (PCI).

The goal of the PRESSS program was to develop a precast concrete construction system that could be used to economically construct tall buildings in regions of high seismicity. From 1993 to the present, BauTech, Inc. has supplied BauGrids® first for extensive testing at the National Institute of Science and Technology (NIST), University of Washington, University of California, San Diego, and then for projects of ever increasing size in California and New York. The BauGrid® Reinforcement System was instrumental in the successful design and construction of the world's tallest precast concrete building in a region of highest seismicity, at 3rd & Mission in San Francisco. The hybrid structural system is composed of frame joints with both mild reinforcement and prestressed reinforcement. The design and construction team put a great deal of thought and effort into not only making the precast structure earthquake resistant but making it constructable. The BauGrid® Reinforcement System proved to be the answer for the need to hold very exact dimensional tolerances so that the precast elements could be fit together rapidly and the prestress strand and mild reinforcement easily installed.

“The PRESSS Hybrid System is due in a large part to the parallel development of BauGrid® Welded Reinforcement Grids by BauTech, Inc.”

----Joe Sanders, Chief Engineer, Charles Pankow Builders

The test of a 5-story HYBRID frame at UCSD demonstrated that a building with HYBRID frames will sustain a minimum of structural damage, even when subjected to very strong ground motion.

According to Charles Pankow Builders, "the Precast Moment Resisting Frame protects the integrity of a building's structural frame through seismic performance." Other advantages include:

· Avoids Loss Due To Expensive Post-Earthquake Structural Repairs

· Design Flexibility

· Shorter Construction Duration

· Better Lateral Resistance

· Floor-To-Floor Height Reduction

· Effective In Mid-rise To High-rise Buildings And Parking Structures"

For more information, log on to www.pci.org and www.pankow.com.

The BauGrid® Reinforcement System (B/GRS) has been specified in increasingly larger projects since 1988, when it was first used as shearwall confinement reinforcement in a 17-story San Francisco State University dormitory after being tested at the University of California, Irvine by Professor Robin Shepherd, and at the University of California, Berkley by Professor Vitelmo Bertero. The excellent performance of the structure during the 1989 Loma Prieta earthquake justified the use of higher ductility factors in the earthquake design, which significantly reduced labor, material and time to construct the 17-story dormitory which has 18 cm (7”) thick bearing/shearwalls. An earlier preliminary design with conventional reinforcement and its consequently low ductility factor design required 25 cm (10") thick walls.

Most recent projects are

1. St. Regis Museum Tower, 42-stories in downtown San Francisco.

2. 680 Mission St. in San Francisco. This 39-story luxury apartment building is the world's tallest precast concrete building in a region of highest seismicity.

3. 24-story Renaissance condominium in downtown San Diego.

4. Plantable retaining wall on Interstate I-125 South by Caltrans.

5. 555 City Center 20 story office building in Oakland, California. Please refer to recent article in F.W. Dodge California Construction Link, May 2002 issue, page 16.

6. Sky Harbor Airport parking structure in Phoenix.