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National Information Service for Earthquake Engineering
University of California, Berkeley

 Development of Structural Members

      From the beginning, Leonhardt, Andrä and Partners have worked on the development and improvement of structural members and details in order to make structures more economic, more reliable, aesthetically more pleasing and less susceptible to damage, and hence to simplify maintenance.  The developments include a variety of prestressing system and ridge cables, bearings, expansion joints, railings, guard rails, etc.

The following are a few of the more than 80 patented devices:

PRESTRESSING SYSTEM ‘LEOBA’

Leonhardt, Andrä and Partners started as early as 1949 to develop and license their own prestressing system.  Under the name of LEOBA (Leonhardt-Bauer, a partner who died in 1978), the following systems were developed:

  • Concentrated tendons for unlimited forces.  The tendons of parallel strands pass around anchor blocks which are forced outwards by hydraulic jacks.
  • S 24 to S 64, for prestressing forces from 21 to 64 tons, consisting of wires 5 to 8 millimeters in diameter.  The fixed end has a bond anchorage and the live end loops around a hammer head.
  • AK 10 to 163, for prestressing forces from 10 to 163 tons, consisting of 1 to 12 bars, 12.2 to 14 millimeters in diameter, with special wedge-anchorages.
  • LZ S 2-6 to 12-6, for prestressing forces 28 to 167 tons, consisting of 2 to 12 strands, 0.6 inches in diameter, with wedge-anchorages.
  • HM 575 to 1100, for prestressing forces of 36 to 70 tons, consisting of smooth bars 26 to 36 millimeters in diameter, with special rolled-on thread anchorage.
  • Thermo bond.  In order to avoid costly and often poor quality grouting, a plastic covering is applied to the HM bars.  During installation and stressing, it permits relative displacements between concrete and bar, but when heated it becomes stiff and can transmit shear forces.

H117.  Spring wedge coupling for tendon AK 124 which avoids losses due to shrinkage and creep in the coupling zone.

The following is one of many papers written on the LEOBA prestressing  system:

Ref:  Leonhardt, F.:  Prestressed Concrete.  Design and Construction.  Verlag Wilhelm Ernst und Sohn, Berlin, Munich, 1964, pp 73 ff, 110 ff, 127 ff, 134 ff, 141, 153, 235.

 

H118.  Exploded drawing of anchorage.

PARALLEL WIRE CABLES

Until about 1965, the cables of cable-stayed bridges and medium span suspension bridges were almost exclusively locked coil ropes.  These ropes have certain disadvantages, such as low fatigue strength, variable modulus of elasticity and poor corrosion protection (which necessitated the reroping of several bridges).

Starting in 1960, Leonhardt, Andrä and Partners developed, together with BBR of Zurich, the shop fabricated parallel-wire cable consisting of:

  • Large bundles of cold-drawn wires with diameter of 7 millimeters (1/4 inch), thus far to a maximum of 337 wires.
  • Corrosion protection by polyethylene pipe, the voids filled with cement mortar.
  • The HiAm (high-amplitude) anchorage, formed by a conical socket and filled with hard steel balls, zinc dust and epoxy resin.

Extensive static, fatigue and corrosion protection tests and practical experience in numerous bridges and buildings demonstrate that these cables are far superior to locked coil ropes.

References: 

Leonhardt, F.:  “Kabel mit hoher Ermüdungsfestigkeit für Hängebrücken (Suspension Bridge Cables with High Fatigue Strengths),”  Preliminary Publication to the IABSE 9th Congress, Rio de Janeiro, 1964, pp 519-524.

Andrä, W. and Zellner, W.:  “Zugglieder aus Paralleldrahtbündeln un ihre Verankerung bei hoher Dauerschwellbelastung (tension Members of Parallel Wire Bundles and their Anchorage for High Fatigue Loads),”  Die Bautechnik 46 (1969), pp 263-268 and 309-315.

Andrä, W. and Saul, R.:  “Versuche mit Bündeln aus parallelen Dr&$228;hten und Litzen für die Nordbrücke Mannheim-Ludwigshafen und das Zeltdach in München (Tests with Bundles of Parallel Wires and Strands for the North Bridge Mannheim-Ludwigshafen and the Tent Roof at Munich),”  Die Bautechnik 51 (1974), pp 289-298, 332-340 and 371-373.

Andrä, W. and Saul, R.:  “Die Festigkeit, insbesondere Dauerfestigkeit, langer Paralleldrahtbundel (The Strength, Especially the Fatigue Strength, of Long Parallel-Wire Cables),”  Die Bautechnik 56 (1979), pp 128-130.

Zellner, W.:  “Kunststoffe als Hilfsmittel für hochfesten Seilkopfverguss und als Korrosionsschutz (Plastics as Help for High-Strength Cable Castings and as Corrosion Protection),”  VDI-Berischte Nr. 225 (1975), pp 51-62.

 

SHEAR-STUD RAILS AGAINST PUNCHING FAILURE OF FLAT SLABS

H119.  Shear-stud rails in flat slabs, Electrical Engineering Faculty Building, Stuttgart University.

  • Large concrete slabs have formerly been designed with mushroom-heads to prevent punching failure, or with floor joists.  Both solutions are expensive.
  • The response of Leonhardt, Andrä and Partners to this problem is the use of shear-stud rails for flat slabs.  The specially designed shear studs prevent punching of the slabs around the columns.

References: 

Andrä, H. P.:  “Dübelleisten zur Verhinderung des Durchstanzens bei hochbelasteten Flachdecken (Shear-Stud Rails to Avoid Punching of Highly Loaded Flat Slabs),”  Die Bautechnik 56 (1979), pp 244-247.

Andrä, H. P.:  “Zum Tragverhalten von Flachdecken mit Dübelleisten-Bewhrung im Auflagerberich (On the Load-Carrying Behavior of Flat Slabs Reinforced with Shear-Stud Rails around Columns),” Beton- und Stahlbetonbau 76 (1981), pp 53-57 and 100-104.

 

H120.  Comparison between a traditional roller bearing and a Neopot sliding bearing for a load of 2500 tons and a longitudinal displacement of ±10 centimeters.

NEOPOT SLIDING BEARINGS

  • Traditional steel rocker and roller bearings were characterized by concentrating the bearing forces at a single point or line.  This concentration required large structural depth, much high-quality material and precise machining.
  • The response of Leonhardt, Andrä and Partners to this problem is the Neopot Sliding Bearing.  The rocking is achieved by the deformation of a thick soft disk of neoprene embedded in a steel pot, and the movement occurs between a lubricated disk of teflon and a stainless steel plate.  Neoprene and teflon work at allowable concrete stresses, so that the load is much less concentrated than in traditional bearings.
  • These bearings were the key to the incremental launching of bridges (see Incrementally Launched Bridges) and to the lateral shifting of the Oberkassel Bridge (see Slides H43-H45).

References: 

Leonhardt, F. and Andrä, W.:  “Stützungsprobleme der Hoch strassen brücken (Support Problems of Elevated Highways),”  Beton- und Stahlbetonbau 55 (1960), pp 121-132.

Andrä, W. and Leonhardt, F.:  “Neue Entwicklungen für Lager von Bauweken, Gummi- und Fummitopflager (New Developments for Bearings of Structures, Rubber- and Rubber Pot Bearings),”  Die Bautechnik 39 (1962), pp 37-50.

Leonhardt, F.:  “From Past Achievements to New Challenges for Joints and Bearings,”  Proceedings of World Congress on Joints and Bearings, Niagara Falls, September 30, 1981, pp 735-760.

The University of California, Berkeley
Copyright 1997, The Regents of the University of California.
Structural Engineering Slide Library, W. G. Godden, Editor
Set H:  Structures of Leonhardt, Andrä and Partners

 

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