基于历史地震记录的楼面加速度放大系数研究

楼面加速度放大系数(FAA)是房屋在地震作用下楼面加速度峰值与地面加速度峰值的比值，反映了建筑主体结构对地面加速度的放大作用，在对建筑非结构构件进行抗震承载力计算时，FAA是必需的重要参数之一。对于FAA的合理取值方法，当前规范大都基于少量的历史楼面地震记录或者简单房屋结构有限元模型，开展统计和计算分析，难以反映各种建筑结构FAA的实际分布特征，使得计算获得等效地震力与其非结构构件实际承受的地震作用相差较大。以美国加利福尼亚强震记录数据库(CSMIP)为基础，以新的建筑高度分类方法为基准，分别计算得到混凝土结构、钢结构和砌体结构房屋的FAA。数据分析结果表明，现行规范难以合理地包络实际观测得到的FAA值。因此，采用抛物线模型，分别拟合FAA沿建筑高度分布曲线，并针对不同的高度类型和结构类型，分别给出对应的曲线参数。所拟合的曲线能够很好地反映出实测FAA分布特点。此外，对于屋面附近的楼层，建议适当提高FAA数值以反映高层建筑中楼面鞭梢效应而造成的突变。最后通过对建筑结构高度进行分类来考虑自振周期对FAA的影响。

Floor acceleration amplification factor in the instrumented buildings #br# under historical earthquake excitations

Floor acceleration amplification (FAA) factor is the ratio of the peak floor acceleration to the peak ground acceleration. FAA represents the amplification effect of the main structure with respect to the ground motion, and is one of the critical parameters in computation of the equivalent seismic force of the nonstructural components installed in each floor level of the main structure. Current code provisions are mostly based on the limited historical earthquake records and finite element model of simple building structures, so that they are not qualified enough to represent the actual FAA distribution profiles in various buildings. Subsequently, the computed equivalent seismic force is quite different from the actual inertia force subjected by the nonstructural component. Using the floor motion records of California Strong Motion Instrumentation Program and new building height classification standard, FAAs in concrete, steel, and masonry buildings were computed and the results show that current code provisions on the FAA cannot effectively envelop the measured ones in a reasonable extent. Parabolic curve was applied to regressing the FAA data and the corresponding parameters were provided to the concrete, steel, and masonry buildings with various height levels. Due to the whip effect, the FAA near the building roof is usually much larger than that in other stories, therefore, a supplementary FAA branch was suggested for the tall, and very tall buildings. At the end, the effect of the vibration period of the building on the FAA was considered in terms of height levels of the buildings. This study can be referred to by the coming code revisions and shall be helpful to designers and researchers.