Proposal of new system of steel supports for space frames and its proof of effectiveness for refraining from damage due to earthquake

The in-depth contents
Publication year 2018
PDF Download
Title Proposal of new system of steel supports for space frames and its proof of effectiveness for refraining from damage due to earthquake
Author Shiro Kato, Takafumi Deguchi, Shoji Nakazawa
Summary The space frames with a flat roof is a common type of roof structures applied to skeletal-membrane structure. This type is also often applied to school gymnasia and city sport halls. In most cases, this type of sport halls are supported by reinforced concrete sub-structure of relatively high and heavy concrete columns or walls, and pin supports or roller supports are applied at the base of steel roofs just atop the reinforced concrete sub-structures. Focusing on the damage experiences due to strong earthquake, failure of not only base mortar and anchor bolts at the support shoes but also steel members near supports have been witnessed. The reason of this type of failure might be classified into two cases. (1) In one case, the shortage of length for lose halls at the base plates. The length is usually adopted like 50mm at both side excluding anchor bolts, however, severer earthquakes might have cuased an exceeding slide over the design length, leading to collision between supports of upper sturctures and anchor bolts/base plates. This collision must have led failure to base mortar and anchor bolts. (2) In another case of pin or roller supports, the seismic forces of heavy reinforced sub-structures or the collision must have been enforced through support shoes into steel member near supports, leading to buckling of steel members or failure of connection bolts between steel members.
The present paper proposes a simple and effective support system to refrain from such kind of failure. The system adopts bending steel columns that are just connected directly with reinforced concrete columns as a sub-structure. It needs no lose halls, and it requires, for each reinforced concrete column, a ductile steel column with prescribed bending capacity. The steel column is connected with the concrete column at the base, and is connected at its upper node as a pin with steel members for upper space frames. Several examples are shown to prove the effectiveness of this system for damage reduction and summarized to derive seismic forces induced into supports and space frames including reinforced sub-structures.