Proposed Design and Method for Providing Sealed Joint Performance under Relative Story Displacement

ABSTRACT: The fatigue resistance of sealed joints to relative story displacement movements caused by earthquakes was studied experimentally and analytically, and the new joint design method was proposed, providing adequate sealed joint performance over the joint’s service life. First, the story drift Я of a curtain wall panel and the number of movement cycles of relative story displacement at a sealed joint over its service life were investigated using earthquake data of the Japan Meteorological Agency. The results indicate that the number of cyclic movements at a sealed joint over its service life is inversely proportional to the story drift of the adjacent curtain wall panels. In regions where earthquakes are numerous, R=1/300 cyclic movements of the total length of the curtain wall panel occur several thousand times over a period of 75 years, while R=1/100 cyclic movements occur only several tens of times. Second, the three criteria required to create a joint design method were investigated, i. e,, type of sealant, effect of cross-sectional size and shape of the sealed joint, and fatigue resistance of the sealant at intersectional zones of sealed joints to the sliding and rocking motions of curtain wall panels. It was obvious that the fatigue resistance of sealed joints was lower in the intersectional area than in the linear sections of the joints, and was lowest in the event of the same movement occurring in both vertical and horizontal joints. The fatigue resistance of a sealant at the intersection of sealed joints is not sufficient to attain the targeted service life and the fatigue resistance of this area of the sealed joint must be improved by applying larger curvature radii at the corner of the curtain wall panel. Finally, the new joint design process for the linear section and the intersection of the sealed joints to relative story displacement movements was developed based on the experimental data. Further, we proposed the methodology to estimate the expected service life of a sealed joint.

KEYWORDS: sealant, performance, design method, relative story displacement, movement, fatigue resistance

Introduction

In sealed joint design [1], fatigue resistance against both extension-contraction movements and shear movements (relative story displacement) needs to be considered. In Japan, where there are many earth­quakes, it is especially important to evaluate the fatigue resistance of sealed joints to relative story displacement. In the aftermath of the 1995 earthquake in the southern area of Hyougo prefecture in Japan, the design method used specified a performance standard for a seismic-proof structure, introducing re­quirements for steel structures or curtain wall panel systems, and, consequently, building service life began to be defined [2-5].

The fatigue resistance of sealant to relative story displacement is affected by the story drift (R), which defined as the relative displacement of a curtain wall panel over the panel beneath it and is calculated as R=8/H (8: story drift movement, H: curtain wall panel height).

The sealed joint design method considers only R= 1/300 relative story displacement of a curtain wall panel and only allows the use of sealants in sound conditions, after testing for R= 1/300. However, when considering the targeted service life of a sealed joint, there is the possibility for displacements of the curtain wall panels to be larger than R= 1/300. Thus, it is important to evaluate the fatigue resistance of sealants to relative story displacement when story drift is greater than R= 1/300. In the current study, the fatigue resistance of sealed joints to relative story displacement movements caused by earthquakes was evaluated using a fatigue test, and a new joint design method was proposed, providing adequate sealed joint performance over the targeted service life.

TABLE 1—Factors evaluated in this study.

Factors influencing performance

Evaluated Factor

Sealants

Two-part building sealants

Grass-section type of sealants

Cross-sectional size of sealants

(joint width and depth of sealants)

Cross-sectional shape of sealants

Type of scaled joints in building

Linear sectional area of the sealed joints

Intersectional area of the sealed joints

Sliding motion type Rocking motion type

Concept of Design Method Providing Adequate Sealed Joint Performance Over Service Life