QUEST RESEARCH JOURNAL, VOL. 18, NO. 2, PP. 1–10, JUL–DEC, 2020 1 Effects of Soil on the Seismic Design of Long Span Steel Frames Using Con- temporary Building Codes Muhammad Tayyab Naqash * , Qazi Umar Farooq 1 Department of Civil Engineering, Faculty of Engineering, Islamic University Madinah, Prince Naif Ibn Abdulaziz, Al Jamiah, Madinah, KSA * Corresponding author: engr.tayyabnaqash@gmail.com Abstract Seismic excitations and other lateral dynamic distress cause the structure’s foundation to interact with the super- structure’s response. Consequently, the surplus stress distribution takes place. This disturbance in the lateral stiffness of the system can cause un-satisfaction with the adopted code provisions. In the above scenario, soil structure interaction of the Moment Resisting Frames (MRFs) becomes very crucial. This article deals with soil stiffness on the long-span MRFs designed with two modern building codes, namely Saudi Building Code (based on American Standards) and Eurocodes. High and medium ductility with parameter and spatial frame configurations are considered in this study. Each frame is analysed considering the foundation stiffness, calculated based on FEMA recommendations. Hence, a total of 18 cases are examined, conducting a modal response spectrum analysis. The period, top displacements, reactions, and damageability criterion for the analyzed frames are compared. It is shown that the consideration of SSI (Soil Structure Interaction) is paramount for frames with such spans, especially when subjected to high seismic forces. Keywords—Seismic codes, soil structure interaction, drift criteria, fundamental period, Saudi Building Code, Eurocodes, moment resisting frames ✦ 1 Introduction L ateral forces induced from ground motion and wind are the primary reasons for the building vibrations. The mechanism that influences the mid to high-rise structure’s vibration characteristics is the dynamic Soil-Structure Interaction (SSI), governed by the soil mechanical behaviour. When a structure is subjected to seismic activity, it interacts with the foundation and the soil and changes with the ground motion. This phenomenon is called kinematic inter- action and becomes essential when the foundation’s stiffness is different from that of the ground. Kinematic interaction substitutes and increases with the size of the foundation. Rigid steel frames have a high fun- damental period due to their flexibility. The situation becomes worst in long spans when flexural governs the design. Steel gives the possibility of a perimeter and spatial framing system. When the perimeter framing system is adopted, the drift limitations are difficult to be fulfilled, especially with Eurocodes. Eurocodes suggests three limits, namely L1 (0.01h approximately ISSN: 2523-0379 (Online), ISSN: 1605-8607 (Print) equivalent to the SBC counterpart), L2 (0.0075h), and L3 (0.005h, quite strict limits, used when brittle materials are used for fa¸ cade) [1][2]. Long span framing configuration is typical in the United States, as generally, the bending effect governs the frames. Since the exterior spatial frame’s contribu- tion to vertical loads is smaller than the interior frame, the outer frame contributes more to the lateral loading due to the torsional effects. Such a pattern is typical in Europe and Japan, with limited bay width, which might be due to strict drift limit. The super-structure mass transmits the inertial force to the soil, causing further deformation in the ground, termed as inertial interaction. This phenomenon is vital with increasing mass and is always predominant than the kinematic phenomenon unless it is a very rigid, extended plant or underground structure. Many researchers dealt with the analysis of struc- tures considering the effect of soil on the structure in earthquakes. For example, using Eurocodes, Minasidis et. al. [3] designed 36 planar moment resisting steel frames and examined under the action of 60 near-fault