Production Plant Wilkhahn Bad Mnder

Thomas Herzog

Subject | Industrial buildings, if they are not merely intended to house large machinery, are mostly designed to shield extensive production or storage areas from the weather. The underlying idea is to provide a horizontal covering over a working environment made up of repetitive units which can be reproduced or subdivided. Therefore, industrial buildings are often flat boxes with the administrative and communal facilities incorporated or appended at one end. As production expands so does the building - augmenting the existing form just like the extended production lines. And as restructuring of production processes is not unknown, working areas must be kept suitably neutral. This frequently results in architecturally undistinguished structures.

However, many industrial companies call for an additional factor to be taken into account in the design of their premises - an unmistakable symbolic characteristic, a "distinguishing feature" expressed in an individual and coherent architectural style. On the other hand, other companies prefer to give each expansion project a new face, planned by a different architect, as an expression of respective contemporary trends. The Wilkhahn company, a leading international manufacturer of chairs and seating, took this approach with its first building in the early sixties. The most recent projects were the production buildings designed by Frei Otto in 1987 and those described here designed by Thomas Herzog in 1992, themselves capable of further expansion. While the interesting suspended shells were the dominant features of the Frei Otto structures, the main focus in Thomas Herzog s low-energy, resource-sparing structure is the emphasis on ecological aspects, both in the design of the building and the choice of materials. In this sense timber represented an excellent choice of building material - a material which Thomas Herzog knows very well, having had many years of experience working with it.

Design | The architect's initial idea was to characterize the solidarity of the workforce, how they stand united, "guarding" the intervening production areas. The sketches of the architect reveal the further evolution of this idea. At the front of the building, four loadbearing two-legged "trestles" (H-frames) are shown spaced


Wilkhahn Wilkening & Hahne GmbH, 31848 Bad Münder-Eimbeckhausen, Germany


Wilkhahn Wilkening & Hahne GmbH


Prof. Thomas Herzog, Architect BDA, Munich, with Bernd Steigerwald

Planning, Tender Documentation, Site Management Architekten Haag, von Oh-len, Rüffer und Partner, Bremen, with Dipl.-lng. Holger Gestering

Structural Engineer Dipl.-lng. Sailer + Stepan, Munich

Timber Engineer

Johann Hocke GmbH & Co.,


Windows, Façades LANCO Lange Fenster- & Fassadenbau, Göttingen

Date of Completion 1992


The total cost was 15.5 million DM including the reinforced concrete basement and the parts connecting the new and old buildings.

Energy Plant For Wilkhahn Section

7 | The production building from the south-west. The trussed edge beam of the roof oveT the production bay is in front of the plane of the facade. Thus the structural system becomes apparent.

10 I Production bays and intermediate H-frame blocks after completion of the roof panels. Visible here are the camber of the trussed beam in the centre of the production bay and the round steel sag rods.

8 I Constructing the first two (northern) H-frame blocks with the production bay roof suspended be-

58 tween.

9 I The H-frame is assembled in a horizontal position on site. Visible here are the lateral protections of the intermediate rail, the fixings for the bracing and the curved roof beam at the top.

11 | Structural details of H-frame, scale 1:50. Vi: Base with concrete plinth. Hi: Horizontal section through Vi. V2: Frame at intermediate-rail level showing support for production area roof beam. H2: Horizontal section through V2. V3: Section through intermediate rail. V4: Elevation of bracing crossover on intermediate rail. V5: Frame at roof level showing hangers. V6: Section through roof beam showing upper part of frame leg in elevation.

Worst Production Plants

30 m apart. These are fixed points supporting the flat roofs over the production bays. The foundation is formed by a reinforced concrete basement which projects out of the sloping hillside and allows for access and storage zones.

Reinforced concrete access and service cores are located within the 5.40-m-wide H-frame blocks. The three large production bays, each approx. 25 x 33 m, receive daylight through the front and rear walls as well as through the continuous areas of glazing provided between the bays and the H-frame blocks; their sloping profile helps to characterize the look of the facade. The flat roofs over the production bays are extensively planted. The depth of the complete building is 33 m, and it is designed in such a way that two further buildings, spaced 13 m apart and with the same layout, can be added at the rear. Both the production bays and the intermediate H-frame blocks are based on a 2.70 x 6.60 m grid, although for structural reasons the 5.40-m-wide H-frames (2 x 2.70 m) are offset from the grid by 150 mm with respect to the production bays.

Structure | The desired building profile and the decision to employ timber had a number of consequences. The large-span roofs to the production bays were planned with glulam sections with a structural depth of 1500 mm and trussed with sag rods. The total span of 24.30 m was then shortened by suspending the start of the trussed section - 2.70 m away from the support - from the H-frame. Trussed beams, however, tend to deflect severely under load. This is also true for the H-frame bracing. A structural analysis revealed that in the most unfavourable loading case the roofs over the production bays deflect by up to 60 mm and that the H-frames deform correspondingly! This deformation had to be taken into account when detailing the junctions with the facades and roofs. It also led to the tapered strengthening of the H-frame legs by 300 mm at the level of the production bay roof, where the greatest bending moments occur.

The H-frames: Other details of the structural members evolved purely out of the possibilities offered by the use of glulam sections. For example, the main loadbearing elements, such as H-frames and roof beams, are triple compound sections whose joints can be ideally designed to suit timber. Each leg of the H-frame comprises two 250-550 x 150 mm sections with 200 x 200 mm spacer blocks between so the total width of this compound section is (2 x 150) + 200 = 500 mm. The intermediate rail is 620 x 200 mm, passes between the leg sections and projects 460 mm beyond to act as a support for the roof. The intermediate rail of the H-frame is at the level of the production bay roof. The frames stand on 1050-mm-high reinforced concrete plinths to protect them against impacts. The curved roof beams at the top do not form part of the structural frame; one end is supported on sliding bearings which prevent internal stresses at the calculated outward bending of the legs under load. The frame is stabilized by 36 mm dia. steel bracing. The upper ends of the bracing join the legs at the point where the roof beam hangers are attached, i.e. 1585 mm below the top of each leg. At this point there are common gusset plates which transfer the tensile and compressive forces via steel dowels into the legs. However, the round-bar bracing is not a simple cross. The ties are cranked because the crossing point is located in the centre of the intermediate rail where there is an appropriately shaped gusset plate. Structurally somewhat more complicated but considerably more convincing aesthetically!

Trussed roof beams over production bays: The trussed roof beams over the bays are also triple compound sections like the H-frame legs. At the supports they are placed like a fork around the cantilevered "tenon" of the intermediate rail, to which they are fixed using steel dowels. They are glulam beams with a depth of 720 mm at the supports and 900 mm in the centre of the span in order

Framing Canti Levered Bay Window
12 I The roofs over the production bays are extensively planted. Visible here is the slight rise of the roof beams to provide drainage for the roof planting. The sloping glazing adjacent the H-frame blocks is provided with ventilation louvres.

13 I Detail of junction between facade and roof beam over production bay, scale i:io.The tight sliding joint between window facade and beam allows for the movement resulting from the beam deflection under load. The façade is supported by the lightweight steel frame behind, which is at the top propped against the roof and connected via elongated holes.

Cable Handrail Construction Detail

16 | Detail of connection between rail construction at the panel and the intermediate rail, scale i:io.

Timber Railing Construction Detail

14 | Section through façade to production bay, scale 1:50. The façade is of timber-stud construction comprising 100 x 60 mm glulam members. Behind, bracing made from lightweight steel sections.

15 | Section through south elevation, scale 1:50. The panels in the timber-stud wall (consisting of 160 x 60 mm glulam members) are constructed as follows: 20 mm plywood, vapour barrier, 135 mm thermal insulation between 135 x 40 mm framing, protective sheeting, 10 mm battens, 123 x 21 mm lapped larch weatherboarding.The roof construction is not illustrated.

16 | Detail of connection between rail construction at the panel and the intermediate rail, scale i:io.

to create a fall for draining the roof with its extensive planting. The underside of the beam also has a 90 mm camber at the centre of the span so that under full load (60 mm deflection!) a slight rise still remains, thereby countering the visual effect of the deflection. The outer members of the edge beams are 480-660 mm deep, the middle member 720-900 mm. The sag rods - St52 steel bars, 52 mm dia. - are placed centrally under the whole cross-section and hence immediately in front of the facade. All the other beams consist of two 720-900-mm-deep outer members which are connected together flush at the top by means of 200 x 200 mm spacer blocks. Each of these beams is provided with two 36 mm dia. steel sag rods, placed centrally under the outer members. These round bars are fitted with left-hand/right-hand threads to enable subsequent adjustment. They are connected via cast-iron forked ends to steel gusset plates which are in turn fixed to the timber beams by means of steel dowels.

Roof construction, production bays: To carry the roof construction, 480 x 120 mm glulam beams are fixed at 2.70 m centres between the trussed main beams and flush with the tops of these beams. The roof itself comprises 2.70 x 6.60 m bonded panel elements which are 172 mm thick in total. They are covered with 16 mm plywood on both sides and inside contain 140 x 40 mm timber sections at approx. 400 mm centres in the loadbearing direction with 140 mm thermal insulation laid between. A vapour barrier is provided on the underside. The edge panels overhang the facade by 800 mm and are correspondingly wider. This construction serves as a base for the approx. 120-mm-deep substrate for the extensive roof planting. To drain the roof, a slight rise is provided in the middle such that even under loading the lowest edge is still in front of the windows in the H-frame blocks.

Roof construction, H-frame blocks: Here too, the roof consists of large-sized panels, in this case consisting of 100-mm-deep timbers in the loadbearing direction covered with 16 mm plywood. These elements span 5.40 m, are supported on the edge beams between the legs of the H-frames and are pre-shaped to a radius of 15 m. After laying, battens and counterbattens are fixed on the upper surface ready to receive the roof covering of curved, profiled steel sheeting. After attaching the roof covering, 100 mm thermal insulation is fixed to the underside with a vapour barrier beneath, fixed to the loadbearing members. Finally, thermal insulation between 40 mm battens onto which the plasterboard ceiling is fixed. Positioning the vapour barrier between the layers of insulation enables pipes and cables to be laid behind the plasterboard without damaging the vapour barrier.

The facades: The east and west elevations of the building consist of a timber-stud construction utilizing glulam members. In the production bays, welded lightweight steel sections are placed behind the posts to carry horizontal loads. Most of the long elevations comprise thermally insulated, translucent panels (U-value 1.7 W/m2K). The solid panels on the north and south faces are provided with lapped larch weatherboarding externally and 20 mm coated chipboard internally (U-value 0.3 W/m2K).

Worst Production Plants
17 | Erecting the first roofing panel on an H-frame block. The projecting timber members are for the overhanging eaves at the gable.
Form Panel Plant

1 | The original design, which was not realized in this form, had deep, cable-stayed girders.

2 | Elevation, scale 1:500. On the right with, on the left, without the side cladding and balustrading. The cantilever joints are situated 7 m beyond the intermediate piers.

3 | Detail of side elevation, scale 1:30.

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