Usage of glued laminated timber in modern architecture

Church of the Merciful Heart – KVP Housing Estate, Košice

Architects: M. Drahovský, L. Friedmann, R. Neufeld, P. Pásztor, R. Rozman, P. Šimko
Investor: Roman Catholic Parish Košice
Project, supply, and installation of wooden structures and cladding: TAROS NOVA s.r.o., Rožnov pod Radhoštěm

Construction history:
1995-1999     individual stages of project documentation
1999-2001     construction of part of the church (RC structure of the nave and tower)
2001-2007   work on the nave and tower nearly halted (for financial reasons)
2002-2007     construction of the parish pastoral center
2007-2010     completion of the RC core of the church tower
2010-2011     implementation of the wooden structure of the tower and nave of the church
2011          realization of the exterior cladding made of TiZn sheet metal and internal wall coverings

The history of the church's construction dates back to 1995, when a competition was held for the urban planning and architectural design of the parish church and presbytery in the western part of Košice known as the KVP housing estate, which is also referred to as the Košice Government Program. The area is located approximately at the midpoint of the eastern side of the main transport artery of the housing estate. The winning proposal was particularly attractive for its urban concept, where the ensemble of objects - the nave of the church, the sacred tower, the presbytery building, and the pedestrian footbridge - is organized around the square in such a way as to define the “wall” of the square. This elevated, open space (due to the level of busy traffic) is perceived partly as public (interchange of pedestrian paths) and partly as semi-public, possessing a certain atmosphere of sacredness. This arrangement is intended to also facilitate the church's opening up to the lay public. The transport corridor (a four-lane road) is understood as a “noisy flow – river,” spanned by a footbridge, on the bank of which lies the nave ready to “set out to fulfill the expectations of the faithful.” Entrances to the buildings are on the opposite side – from the less noisy square.

Technical parameters and characteristics of the church nave:
Plan dimensions of the nave:    32.0 m (length) x 22.0 m (maximum width)
Height of the nave at the front:                 17.4 m
Height of the nave at the entrance:              9.2 m
Load-bearing structure up to +4,000 m:     reinforced concrete structure with infill masonry
Load-bearing structure from +4,000 m:     wooden structure made of glued laminated timber

Technical parameters and characteristics of the church tower:
Plan dimensions of the tower:     13.5 m (length) x 7.6 m (maximum width)   
Height of the tower:                             33.15 m
Load-bearing structure of the tower: reinforced concrete structure (RC monolithic core up to +22,000 m)
Load-bearing structure of the cladding from +9,000 m: wooden structure anchored to the RC monolithic core of the tower

Description of the structure – church nave
The wooden structure of the church nave has maximum plan dimensions of 32.0 x 22.0 m and features a complex geometric shape, defined by lines curved in multiple planes. The height of the roof at the front of the nave is +17.400 m and at the rear +9.120 m. The main load-bearing structure consists of atypical wooden trussed frames spaced at intervals of 1.200 m (axis 1-26), which are anchored at level +4.000 on the RC ring beam. The original design concept has been preserved, but due to the passage of approximately 15 years between the design and construction phases, some technical adjustments to the structural and material solutions were made. Standard cut elements were replaced with glued laminated timber, which at the time of the initial design work was financially unthinkable. Nowadays, glued laminated timber is more financially accessible, making this change advantageous from both a visual and structural perspective.

Shape of a typical truss

Static calculations verified the original designed solution. It was already known that individual transverse frames could not function independently due to significant concentrations of force effects at the upper part of the interior columns. Therefore, it was necessary for the individual frames to be connected by a rigid roof plane, which allowed for the transfer of horizontal effects into the RC bracing elements (the RC portal wall at the entrance and the RC wall of the sanctuary at axis 7). Here, a modification of the original solution was also made, which comprised bracing in the roof plane consisting of steel diagonals and strap elements. Since this solution proved to be problematic for assembly, these elements were replaced by glued rafter furring braces hidden within the roof cladding, which were mutually connected by steel rods. Horizontal effects are transferred via the rigid roof plane to the bracing in axis 7 and the RC portal wall. The horizontal forces are transferred from the bracing in axis 7 to the RC wall shaped like an “M” forming the altar. Part of the horizontal forces is also transferred to the frontal RC pillar at axis 0 and to the corner RC pillars at axis 24’.
                  
Static calculations practically confirmed the profiles of individual elements from the previous design. For the main interior columns, only the profile was adjusted from an architectural perspective. Instead of the anticipated columns made of round timber, columns were made of glued laminated timber in the shape of an “x-edge” to enhance the impression of a raw (technical solution).
From a static perspective, the individual parts function as a spatial structure composed of individual frames, a roof plane, and transverse elements between the trusses (purlins, roof braces, and braces at the level of the skylights).
The interior columns are anchored to the purlins using steel caps. In the longitudinal direction, the perimeter columns are connected by purlins at two height levels. In the odd modules, the interior columns rest on an RC pillar and in the paired modules on two inclined braces 180/180 and below on a base beam 200/200. The perimeter columns lie on an RC ring beam anchored using steel elements and chemical anchors. The anchoring of the interior columns is solved using vertical connection plates welded to the built-in plates in the pillars. The trusses are further connected with braces in the skylight plane made from a profile 140/140, which are anchored to the RC pillar at axis 24’ and to the frontal pillar at axis 0.

Computational model of the nave

The roof plane consists of reinforcing edges from a profile 770/100 anchored to the purlins using threaded screws and mutually connected by steel rods, ensuring the transfer of horizontal forces to truss 7 and the RC portal wall. The edges are anchored to the portal wall at the upper edge of the wall with chemical anchors through atypical locksmith elements. The structure of the roof further consists of trusses 140/120, ensuring additional longitudinal bracing between the trusses and creating a ventilated gap.
The entire structure is further stiffened by a continuous sheathing of 24 mm thick boards.

Description of the structure – church tower

Computational model of the church tower

The load-bearing wooden structure of the tower's cladding has plan dimensions of 12.80 x 7.70 m (irregular shape) and consists of wooden pressed wall trusses, which are anchored to the concrete core of the tower and interconnected by cut rafters forming the roof of the entire tower.
From a static perspective, the individual parts of the structure act as a spatial structure. The rafters function as simple or continuous beams that transfer loads into the wall elements or directly into the tower core. The wall elements are braced with diagonal bracing planes approximately every 2.5 m. The anchoring of the wooden structure itself is at height level +9.000 on the RC ring of the masonry part of the tower. The entire structure is further stiffened by a continuous sheathing of 24 mm thick boards. The cladding with boards is omitted only in the bell tower part, where metal slats are installed as part of the cladding.

Plan shape of the tower

 Installation of the wooden structure
During the first inspection of the construction site, it became clear that detailed measurements of the completed RC structure of the tower and nave would need to be carried out. Based on this measurement, which represented a challenging task for the surveyors, a revision of the originally designed shape of the wooden structure was made. The geodetic measurements revealed several issues that needed to be addressed in both the design and directly at the construction site. The inaccuracies in execution primarily stemmed from the geometrically demanding monolithic concrete structures. For both the tower and the nave, a primary task was to ensure a seamless transition of the cladding from the wooden structure to the reinforced concrete part with infill masonry. Even before the production of the elements, the shapes of the transverse trusses were adjusted according to the actual measurements to ensure a problem-free transition.

Installation state of a typical truss

The installation of the load-bearing structure of the tower's cladding proceeded gradually by individual floors. The wall truss elements were segmented into individual parts, and additional parts of the individual trusses were gradually added. Each wall element is anchored to the RC core of the tower into an atypical steel shoe using mechanical anchors. The shape of the trusses and the method of anchoring had to be adapted to the actual shape of the RC core of the tower (vertical alignment of the walls, actual plan shape). At the level of each floor, horizontal bracing is carried out. After completing the individual wall elements from the pressed trusses, the roof elements were placed on top, and finally, sheathing for the entire tower was installed. A tower crane and scaffolding were utilized for the construction of the tower's structure throughout the entire perimeter of the tower.
                   

Installation of a truss

The installation of the load-bearing structure of the nave occurred gradually by individual trusses. Each truss was completely assembled on the ground in a horizontal position after thorough re-measurement and was temporarily stiffened for assembly.

It was then craned into pre-prepared anchor steel elements. In this way, the entire structure was gradually erected. Longitudinal structural elements and assembly stiffening elements were progressively placed between individual transverse trusses.
Here as well, the shapes of the individual elements were derived from geodetic measurements. These measurements also showed that the outer columns, which were supposed to run beneath the RC arch of the tower, would be in conflict with it. Ultimately, it was decided, after consultation with the architects and designers of the concrete structure, to anchor these outer columns into the RC arch of the tower and to cancel the columns in the area beneath the arch, further connecting the interior space of the nave with that of the tower.
Cranes and mobile platforms were used for the construction.

Perimeter cladding of the nave and tower
TAROS NOVA was also the supplier of the composition of the perimeter cladding, including the external cladding as well as internal coverings.
The most complex part of the perimeter cladding was executing the roofing work, which gave the entire church its final visual form. The roofing consists of pre-weathered blue-gray TiZn sheet
0.8 mm thick. For the facade implementation, sheets with a nominal width of 570 mm were used, which were modified and bent on-site according to the architectural design into their final shape. The construction of the perimeter cladding required the erection of spatially complex scaffolding around the entire perimeter of the tower and nave with minimal interventions into the cladding itself.