For a quarter of a century, the BESISTA® tension rod systems/tension bar systems have stood as the epitome of innovation and quality in diverse fields of construction. Tension rod systems/tension bar systems and compression rod systems have now become part and parcel of contemporary architectural, steelwork, timberwork, facade, glazing and civil engineering solutions. They have given rise to distinctive, filigree compositions that have not only had a powerful impact on contemporary architecture, but have also furthered the goals of sustainable, resource-efficient construction. BESISTA® designer rod systems excel above all by their supreme quality and tremendous design appeal, with organically flowing transitions between rod and anchor. High safety and absolute reliability are built-in product features. All these benefits have earned the safety systems a global reputation, as demonstrated by their use on a string of prestigious and architecturally challenging schemes in various countries, e.g. the spectacular Metropol Parasol in Seville (Spain), the Skywalk Scheidegg treetop walkway (Germany) or – most recently – the new football stadium in Essen (Germany), Salzburg railway station (Austria) or the impressive viewing tower in Lipno (Czech Republic).
The tension rod systems/tension bar systems originate from an invention by architect and engineer Dr.-Ing. Anton-Peter Betschart. As early as 1981, he set up the Development Institute for Casting and Construction Technology (Entwicklungsinstitut für Giesserei- und Bautechnik; EGB) as a private initiative in Bad Cannstatt, Stuttgart. It was here, at the Institute’s design and development workshop, that the scientific groundwork was performed for the renaissance of cast metals in architecture. Apart from his research, which included investigations into load-carrying capacity and component tests using special apparatus, Betschart focused on the development and realization of cast structures embodying a new formal language. The technical background and a host of ideas for this new stylistic vocabulary are presented in his textbook “New Cast Structures in Architecture”.
Building on further ground-breaking research, Betschart in 1985 invented the world’s first ever tension rod system/tension bar system with left- and right-handed threads, developing it to series production stage in the following year. In line with their function, the castings connecting tension rod/tension bar and gusset plate were christened “rod anchors”. Unlike conventional tension rods/tension bars, his system is tensioned by turning the tension rod/tension bar. The attractively crafted rod anchors (fork heads) represent the successful marriage of diverse criteria governing safety, performance, manufacture and formal design. Tracing the lines of force, the contours of the filigree castings merge almost seamlessly with those of the tension rod/tension bar. The delicate ribs on the rod anchors fulfil a number of vital functions: they guarantee perfect forming and casting, make up for the cross-sectional area lost due to the safety-relevant inspection hole, form the unique wrench flats on the lip at the shaft ends and prevent any wear of the designer contours during production.
In 1987, Betschart was granted the first utility model for his invention and, finally in 1989, the first patent for the “rod anchor”, the centrepiece of his tension rod systems/tension bar systems and compression rod systems. After relocating to the Swabian town of Bad Boll in 1990, he pressed ahead with series production of the BESISTA® 355 safety tension rod system/tension bar system. Yet, Betschart was soon to suffer the fate of many a pioneer as others copied his innovative ideas. Subsequent events have nonetheless rewarded his persevering spirit and vindicated the age-old wisdom that “You can’t beat the original”. The name “BESISTA®”, an acronym of “BEtschart-SIcherheits-STAbsystem” (Betschart safety rod systems), was registered as a trademark in 1991.
BESISTA® has been at the forefront of research and development in the field of tension rod systems/tension bar systems and compression rod systems since the very outset. It duly became the first tension rod system/tension bar system manufacturer to successfully apply good-practice galvanizing methods to all system components, including the castings. Most notably, it succeeded in producing rods with a hot-dip galvanized coating on the threads and thereby guarantee optimum corrosion protection. As early as 1991 – in recognition of the complex fabrication process that is the key to the safety rod system’s enhanced sustainability – BESISTA® was presented with the German Galvanizers’ Award by the German Industrial Association for Hot-Dip Galvanizing. Further accolades in the following years testified to the product’s performance, sustainability and design appeal: BESISTA® won a prize in the “Designing with Cast Materials” competition staged by the German Foundry Associations (1993), the German Steel Innovation Award of the German Steelwork Association (1994), and, for a second time, the German Galvanizers’ Award (1995).
In 1991, the forerunner BESISTA® 355 tension rod system/tension bar system was also the first product of its kind to undergo a type stress analysis with type test. Four years later, BESISTA® launched onto the market the series-produced tension rod system/tension bar system made from S460N fine-grained structural steel. In 1998, this became the first such system to be granted a National Technical Approval by the German Institute for Construction Technology (Deutsches Institut für Bautechnik; DIBt) in Berlin. 1999 saw another industry first as BESISTA® switched from S460N steel to the special, optimized S540N fine-grained structural steel developed by Betschart, with a guaranteed yield strength of 540 N/mm². This was the culmination of a chain of improvements – from steel grade S235 through S355 and S460N (fine-grained) to S540N (special fine-grained) – reflecting BESISTA®’s wholehearted commitment to innovation. The company’s pioneering role in the forward-looking and resource-efficient use of materials was duly honoured by the Business Promotion Society of the District of Göppingen with its 2001 Innovation Award. New inventions followed in 2002 in the shape of the BVS 230 and BVS 500 pretensioning systems. These permit the simple, rapid and controlled pretensioning of tension rods/tension bars.
Through continuous refinement, the tension rod systems/tension bar systems and compression rod systems have since evolved into the present-day BESISTA® 540 designer rod system, complete with patents for its numerous innovations. New additions to the extensive product range in 2005 featured cross plates for X-braces with extremely flat angles and compression rod connections with higher-strength threaded pins for steel compression rods. In 2008, the rod systems were granted a European Technical Approval (ETA) by the DIBt. This was accompanied by a CE certificate issued by the Materials Testing Institute University of Stuttgart (MPA Stuttgart). Since then, MPA Stuttgart has been responsible for the periodic external surveillance of manufacturing equipment, internal control and documentation of quality assurance procedures. A suspension system developed in 2008 features special suspension rings that allow the simultaneous turning and tensioning of installed rods. 2009 then saw BESISTA® unveil the first “cross anchor”, which adopts the popular design style of the rod anchor. This was followed in 2011 by the development of compression rod connections with higher-strength threaded pins for timber compression rods. The most recent highlights include “angle anchors”, also styled like the rod anchors, for elegantly crafted bracings and “cross plates” for X-braces with extremely flat angles.
BESISTA® has reaped all the benefits of being at the cutting edge of technology: its products offer supreme design sophistication, maximum safety and absolute reliability, coupled with unbeatable cost effectiveness.
Safety first is the BESISTA® watchword
National and European Technical Approvals bear witness to the top priority enjoyed by safety issues within the overall philosophy of BESISTA® systems. All system components exhibit safety margins that far surpass the minimum permissible values. Similarly, the thread lengths in the rod anchor shaft are 1.4 times longer than required. Moreover, the fork-head opening of the specially designed, patented rod anchor widens on either side of the pin hole so as to accommodate axial deviations in the gusset plate of up to 2°. All these unique features help to boost the overall system safety performance.
In terms of materials, too, quality and safety are the prime consideration. The EN-GJS-400-18-LT spheroidal graphite cast iron used for the rod anchors offers major safety benefits over cast steel, which is prone to cracking due to its extremely high shrinkage. The expansion resulting from the formation of graphite spheroids in the ferritic matrix serves to offset the – in any case, inherently low – shrinkage for this material, thereby successfully eliminating any risk of cracking. Even at low temperatures, this metal grade offers supreme performance thanks to its high ductility, with a minimum elongation at break of 18% in tensile tests, backed up by guaranteed notched impact toughness at -20°C. This is why spheroidal graphite cast iron is used for a wide range of safety-critical components, e.g. in cable car and ski lift installations as well as for heavy-duty chassis elements and coupling plates for motor vehicles.
The special S540N fine-grained structural steel currently used by BESISTA® – which, to rule out any confusion, is supplied as standard for every order – can accommodate 52% higher loads than S355. This allows the specification of thinner rods and smaller rod anchors for greater resource efficiency and sustainability. To prevent hydrogen embrittlement damage during the hot-dip galvanizing process, the softly contoured wrench flats on BESISTA® products are only pressed after galvanizing. Likewise, all threads at BESISTA® are not rolled, but cut with special tools. This is because the high strain hardening at the thread base, caused by cold-forming processes such as rolling, tend to encourage hydrogen embrittlement during hot-dip galvanizing.
Internal and external quality assurance with CE certification account for a major proportion of product costs. External surveillance and the periodic inspection of all BESISTA® products is carried out by MPA Stuttgart. The testing regime involves numerous incoming goods, production and safety checks. This safety consciousness is another key reason why clients, designers and contractors opt for BESISTA®. Fabrication takes place at the company’s own plant, thus allowing consistently high standards of quality, reliability and flexibility to be upheld, to meet even the most stringent demands.
Key benefits for erection
BESISTA®’s installation instructions are backed up by a wealth of illustrations to offer straightforward, easy-to-understand guidance on safe and time-saving assembly. Tension rod systems/tension bar systems and compression rod systems are safety-critical components. Close observance of the installation instructions is thus essential at all times.
The inspection hole, unique to BESISTA® and incorporated not only in the rod anchors but also in cross anchors and tensioning sleeves, plays a pivotal role during erection. It is essential for fool-proof checks on compliance with the required thread screw-in depth. The inspection holes also allow verification that no thread shortening or any other changes take place during assembly, e.g. due to a mix-up of rods or altered hole spacings. This feature also obviates the need for cover sleeves, which are otherwise required to check the screw-in depth. Any cover sleeves used with BESISTA® systems serve only the aesthetic function of masking the threads.
BESISTA®’s development of the patented BVS systems – available in two sizes, BVS 230 (kN) and BVS 500 (kN) – for controlled pretensioning of the tension rods was a further trailblazing achievement. The BVS 230 system allows tensioning to be performed cost-effectively by a single person in a matter of minutes. The fixed connection between pump and hydraulic cylinders allows absolutely hazard-free pretensioning by dispensing with the need for any on-site handling of hydraulic hoses. This helps prevent accidents while ensuring a reliable force build-up and accurate kN readings. The pretensioning systems made their triumphant debut on Leipzig’s Red Bull Arena project, where they were used to tension 320 M45 and M68 tension rods/tension bars at heights of up to 56 m. To certify proper operation of the BVS systems, a conformity document is prepared for the structural engineer and the client both prior to and after hire of the pretensioning equipment.
BESISTA® tension rod systems/tension bar systems cater for very long adjustment distances, equivalent to at least three times the rod diameter, i.e. almost matching those of turnbuckles. This allows the accommodation of large tolerances, particularly with long rods.
Apart from rods, the rod anchors also accept ropes. The first such applications include Leipzig’s Red Bull Arena scheme and the new exhibition halls at Messe Stuttgart, where most of the ropes are connected with BESISTA® rod anchors.
Further benefits for on-site assembly include the accommodation of gusset plate tolerances and the protection of coatings through the specially designed and patented internal fork head faces of the rod anchors.
Award-winning corrosion protection by hot-dip galvanizing
Hot-dip galvanized assemblies are required, for example, for outdoor applications or swimming pools. A so-called duplex (zinc and paint) coating is recommended for particularly aggressive atmospheres. All BESISTA® system components – rod anchors, pins and tension rods – are specially designed for hot-dip galvanizing treatment. This involves a complex fabrication process that earned the company the German Galvanizers’ Award as early as 1991, and again in 1995. To maximize safety, all pins are supplied with a hot-dip galvanized finish, even if only black steel is specified. One unique selling point of the hot-dip galvanized rods is the zinc coat on their threads. Prior to galvanizing, these threads are cut back by the thickness of the zinc coat using special tools and then recut to gauge after coating – an operation requiring expert craftsmanship. The cathodic protection offered by the galvanized rod threads also shields the internal rod anchor threads against corrosion.
The products thus require no sealing or encapsulation, thereby eliminating the risk of uncontrollable moisture inclusions. Nor is the limited thread corrosion protection offered by brushed-on zinc or sprayed-on zinc-rich paint any match for the hot-dip galvanizing process. This issue warrants particular attention during specification and contract award: after all, if “hot-dip galvanized” is specified, then the client is entitled to insist on hot-dip galvanized rod threads.
Fire protection for tension rod systems/tension bar systems and compression rod systems is a frequent subject of queries. Given that all system components – including the cast rod anchors – are ferritic, the same fire protection measures can be adopted as for steelwork. The European Technical Approval (ETA) notes the following: “In terms of reaction to fire, the tension rod system meets Class A1 (non-combustible) requirements”. Nonetheless, the most recent guidelines issued by the fire-protective coating manufacturers should always be observed.
Environment, health and safety
At BESISTA®, environment, health and safety (EHS) issues have a direct bearing on everyday practice. Here too, the high quality standards extend far beyond the norm to meet the stringent requirements of high-spec applications, such as power stations, or the international export market.
The company gives utmost priority to the health and safety of its workforce, and is proud to say that no accident of any note has ever been recorded in its 25-year history. Regular safety drills and healthcare events are just some of the ways in which occupational safety awareness is raised and a healthy lifestyle encouraged.
Moreover, at BESISTA®, we have almost completely achieved our target of generating zero waste during manufacture as a means of protecting our natural environment. For example, metals are fully recycled and wood converted into energy, while cardboard is shredded for reuse in packaging. Even wastewater is filtered and the residue dried into powder by the sun with no external energy use.
New system components recently added to product range
Compression rod connections for timber rods are a further speciality of BESISTA®. These always take the form of two-part connections with higher-strength pins. The tapered machined components can be made from any steel grade in line with the relevant loads. The wide-ranging options available for connection to the wood are specified in function of the particular requirements.
The compression rod connections for steel have been optimized and extended. A total of three variants are available to cater for a wide variety of applications: machined solid rods made of S540N, machined components made of S355 for welding to tubes and machined components with higher-strength threaded pins.
The solid rod variant up to 76 mm dia. is the most economical due to the lack of weld seams and the feasibility of full hot-dip zinc coating while the tube variant is particularly suitable for large diameters. Both the machined components with the threads and the tubes are hot-dip galvanized prior to welding. The machined components with higher-strength threaded pins excel, among other things, by their enhanced stiffness. The connection geometry is the same for all types.
The unique BESISTA® suspension system allows both one-part and extended tension rods/tension bars to be freely turned for pretensioning or post-tensioning at any time. This is not feasible in the case of conventional sleeves with straps (extension sleeves) due to the difficulty of tensioning the rods while pointing the straps upwards. The BESISTA® suspension rings also obviate the need for the coupling and decoupling of rods at the suspension points, thereby achieving additional cost savings. The suspension rings allow easy alignment of the suspended (vertical) rods, which may, if necessary, be secured with locking screws.