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Adaptive Reuse of Clay-Tile Arched Floors | |
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Adaptive Reuse of Clay-Tile Arched Floors Both types of arches were constructed on timber formwork platforms, which were used to secure the tiles in place during construction. The formwork was typically suspended from timber "jack" beams spanning between and over the tops of the supporting steel beams. In a segmental arch, clay tiles were arranged in a shallow profile between adjacent parallel beams. The steel beams were typically held together with tie rods, which helped to resist the outward thrust imposed by the arch on the steel beams, both temporarily during construction and permanently at an end span. Solid clay bricks were also used in a similar fashion; however, hollow clay tiles typically offered an assembly that was not as heavy as solid brick. The flat clay-tile arch transferred the load between the beams, acting as a jack arch with a tapered keystone located at the center of the span. Again, the resulting outward horizontal thrust reaction that occurred at the beams was typically resisted via tie rods that were required both temporarily during construction of interior spans and permanently at end spans. Another type of flat clay-tile arch was the reinforced system. For this type of "arch" system, closely spaced internal reinforcing rods were embedded between the tiles near the bottom, which allowed for the entire section to function more as a true flexural member rather than as an arch. This system was also referred to as the Natco "New York" reinforced flat arch. It served as a precursor to one- and two-way tile joist systems. A third type of clay-tile arch construction includes the Guastavino timbrel arch, which consists of a series of laminated layers of tile slabs that were laid and bonded together with Portland cement mortar to form solid large-span domes. This type of construction was not used in conjunction with steel floor framing, however. Standard flat arches can be classified into two groups: end construction, and combination side and end construction. End construction consisted of laying the axis of the tiles' hollow cells parallel to the direction of the span, except at the center keystone tile. The combination side and end construction method placed the axis of the tiles' hollow cells perpendicular to the span of the arch — i.e., parallel to the span of the supporting beam — for the majority of the blocks used in any one row. In both cases it was normal for the depth of the tiles, in combination with the concrete topping, to be approximately the same depth as the supporting beam. This method of construction assured that the beam was completely braced for the full depth of the steel section and also made it easier to install soffit tiles beneath the beam bottom flange for fire protection. The tie rods used to resist the arch thrust forces were generally placed approximately three inches from the bottom of the beams in flat arches. In the case of segmental arches, placing the tie rod near the bottom of the beams resulted in the tie rod being exposed across the horizontal spring line of the arch. If fire resistance of the tie rod was required, it was more often than not placed higher up from the bottom of the beam, as required to avoid exposure. Typically tie rods were three-quarters of an inch in diameter and were spaced as required to resist the specific thrust of the given arch span, although a minimum spacing of 15 times the width or eight times the depth of the supporting steel beam was recommended. Tie rods at an end span were required as there was no opposing thrust present at the outside face of the spandrel beam. At interior spans, with adjacent arches present on either side, tie rods were only required during construction, but were typically left permanently in place. For this reason, when modifying an existing building constructed with clay-tile arches that involves the removal of an interior span, the capacity of the remaining adjacent span's rods should be verified to assure that the end span conditions created on either side of the new opening will remain stable. The total arch thrust, net area of the tie rods, and maximum spacing for both a flat and segmental arch can be found as indicated below:
Flat arch spans typically varied from three to ten feet and were capable of supporting safe uniform loads between 126 and 1,400 pounds per square foot as indicated in Table 10-31 from the Principles of Tile Engineering: Handbook of Design. Load tables published in Kidder and Parker's Architects' and Builders' Handbook for segmental arch construction list spans up to 21 feet, with load-carrying capacities of up to 485 pounds per linear foot. Table 10-32 from the Principles of Tile Engineering lists spans up to only 10.5 feet. Both of the tables from the Principles of Tile Engineering were based on load tests, which were reduced by a substantial safety factor of seven. When evaluating existing clay-tile arch systems, it is recommended that the initial load capacity rating be based on published tables. >>> Discuss this article in the Architecture Forum...
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