| @ |
ASCE Fall Convention and Exhibit |
|
||||||||||||
| @ |
Use of Glu-Lam Framing in This paper will address itself to the path which was followed by the design team of Harry Weese and Associates, Architects of Chicago and Nishkian, Hammil and Associates, Inc. Structural Engineers of San Francisco in order to arrive at the unusual design solution achieved for the Fredrick E. Terman Engineering Center, Stanford University, Palo Alto. The University’s space requirements were considerable and called for a highly efficient design in order to come within the maximum total budget of $7,000,000.00. Other requirements were that natural ventilation be used wherever possible and that the building be sprinkled throughout. Because of this tight budget, the University originally included a construction company in the design team which filled the role of construction manager and advised concerning materials and type of construction. After the first general meeting or two, a preliminary design utilizing a conventional steel frame was drawn. On the basis of these drawings, a first estimate was made of construction cost. It soon became apparent that the project in its entirety could not be achieved within the budget and a major change would have to be made in the approach. Because steel was at its peak price and timber was near its low price, the Architect and the Engineer met and decided to change the basic structure to a combination of heavy timber construction and reinforced concrete and concrete block. Several major decisions were made concerning changes in the overall design, all with an eye toward economy of construction without sacrificing function. A few of the more important of these decisions included: holding the floor heights in the timber portion to an 8’-8”; using a heavy T & G floor with 1/2 inch plywood and a foamed concrete layer (Elastocell) 1-1/2 inches thick placed on top of the floor for sound deadening and having an exposed underside with most of the pipes and electrical conduits exposed in the wooden portion of the structure; using natural ventilation in the offices, rather than air conditioning, as called for in the University’s criteria. In order to achieve the natural ventilation, corridors are opened to vented skylights in the roof. However, the heating system was so designed that, should cooling be desired in the future, the necessary piping and units are available within the building heating system. This also fits in with the exposed pipes and conduits which allow for easy alteration or future additions. In addition to the above, a structure befitting a prominent engineering school was called for. A structure that would reflect a novel and imaginative design, but still fit in with the high standards of design of the surrounding buildings of the campus. To this, Architect Weese responded with a handsome “L” shaped building that included a large reflecting pool, inside the “L” and at basement level, as an architectural feature. The pool was surrounded by a free flowing concrete retaining walls on the other sides in front of which were retaining walls created from railroad ties stacked and stepped back as they increased in height. Because the area around the pool had existing trees which were to be saved, a system of drilled cantilevered caisson supports 6 feet on center were used, with slightly arched walls spanning between them. This allowed the wall to be constructed without disturbing the existing trees. Strong vertical architectural lines were carried up through the building and terminated with a Spanish tile roof which provided a design linked with the predominant style of the other buildings on the campus. As mentioned above, because of the relatively low cost of structural timber on the West Coast at the time, it was decided to design the building basically in timber. In addition, the result would be an uncommonly large structure for timber and therefore one of unusual engineering interest and would fit it well with the architectural design goals of the University. As the design took form, a five story wood frame with a reinforced concrete two basement structure evolved. The fifth floor was made possible because the building was sprinkled thereby allowing for one more floor than normally allowed in heavy timber. Above the first floor the “L” shaped building had both the long and the short legs of the “L” framed with glu-lam members. The North-South leg of the “L” was 240 feet by 115 feet and the East-West leg was 186 feet by 46 feet (see plate 1). The North-South leg contained a library and auditorium of reinforced concrete construction surrounded by concrete block walls with offices on either side in heavy timber construction. Even though we had made extensive changes in the original concept of design, we were still doubtful that we could get the whole structure within the budget. We therefore made the primary bid package consist of a portion of the North-South leg including the concrete library area and the East-West leg. The alternate consisted of an additional portion of the North-South leg which was 4 stories of heavy timber construction (see plate 1). At this time the university decided to dispense with the services of the construction manager and put the project out for general bids. Needless to say, we were delighted when not only the total building including the alternate came within the budget, but also that some money was left for equipment and furnishings. This economy was achieved not only because of the lower cost of timber, but also because of the faster delivery time, ease of erection, and the ability to use carpenters for the total structure rather than requiring steel erectors for the frames. The design of such a heterogeneous structure presented a number of structural problems. The upper floors were framed with glu-lam members and the ground floor was as well as the two sub-basements were reinforced concrete block walls with poured reinforced concrete flat plates or beams and slabs supported by concrete columns. In the library there was a necessity for some heavy carrying girders to span the auditorium and then four levels up, we again have carrying girders to give a clear span in the top floor as well. It was also an architectural requirement in the timber section to have heavy glu-lam carrying girders (8-3/4” x 36”) at the level of the second floor in order to pick up alternate columns from above. All of the glu-lam frames have been designed for vertical load only and the seismic forces have been distributed to shear wall through out the two wings of the building in addition to the walls of the library core. In order to avoid the creation of heavy lateral torsional forces because of the shape of the building one leg was provided with a complete separation from the other by means of an expansion joint (see plate 1), therefore ending up with the equivalent of two basically rectangular structures. The lateral loads were transmitted to the shear walls at each floor level by the use of the heavy timber floor and the 1/2” plywood diaphragm. The floor was constructed of built-up tongue and groove planks with a net 3” thickness, glued to each other as well as glued and nailed to the frame. (see plate 2). In order to insure that the diaphragm acted as a unit, four of the rows of planks were spliced at all ends with steel straps and heavy bolts so that they could act in tension as well as compression as collectors and chords. The collectors were bolted through the use of bolts and shear angles to the resisting shear walls. (see plate 2). The building below the first floor was of concrete flat plate construction with exterior walls of reinforced concrete block with all cells filled. The basement walls are used as shear walls to resist lateral forces. The first floor slab of the East-West wing extends approximately 29 feet south beyond the building face above to form a brick paved open plaza and the most easterly 26 feet of the first floor of the North-South wing forms a covered brick paved plaza. At the pool end of these plazas there is a continuous wooden bench with foot space outside of the wall. There is a 41 foot wide opening in the East-West wing which extends from the first to the third floor in height, with an open bridge connecting the two separated portions of the second floor of this wing. The glu-lam transfer beams in this area are under the third floor instead of the second. Concrete shear walls around the stairways and elevators and in other strategic locations are used to resist lateral forces above the first floor. Because it was not possible, architecturally, to provide sufficient concrete shear walls throughout the building, 16 gauge steel was used as cladding at the end walls of the legs to develop adequate shear resistance. As stated, the library area contains an auditorium at the first floor level and certain columns from above stop at the second floor, on girders 36: by 48”. This floor is of concrete beam and slab construction as is the roof. The first, third and fourth floors of the core are of concrete flat plate construction. The library area is surrounded by reinforced concrete block walls which not only act as shear walls, but also as a fire separation. Because the glu-lam frames were designed for vertical loads only, it was possible to utilize simple connections. In areas that were not visible, these connection consist of steel plates bent into channel shapes as carriers in order that the members may fit in them and simple through bolts providing the connection (see plate 3). In the areas visible from the outside, the connectors were designed with a single steel plate being inserted into a saw cut in the beam, the bolts going through this plate being countersunk at each end and then covered with wood plugs in order to present an integral wood surface. (see plate 4). To summarize: (1) By an imaginative use of readily available, common materials in the design, combined with an equally imaginative contractor who was receptive to such ideas as the novel method of pre-assembling each five story bent on the ground and then lifting it into place, it was possible to present the client with the full facility desired and still build it within budget. (2) The building was not only brought in within budget, but the end result was as esthetically pleasing as it was functional. Resorting to glu-lam framing was not a sacrifice to the budget. On the contrary, the exposed framing was entirely benefiting of an engineering building for a first line engineering college.
|
|
||||||||||||
| @ | @ | @ | ||||||||||||
