Contents lists available at ScienceDirect Engineering Structures journal homepage: www.elsevier.com/locate/engstruct Effective live load mass for storage buildings on friction-pendulum isolators Juan C. Reyes a , Marco T. Herrera b , J. Paul Smith-Pardo c, ⁎ , Laura S. Córdoba d a Department of Civil and Environmental Engineering, Universidad de los Andes, Bogotá, Colombia b Department of Civil Engineering, Universidad de Piura, Piura, Peru c Department of Civil and Environmental Engineering, Seattle University, Seattle, USA d Department of Civil and Environmental Engineering, Universidad de los Andes, Bogotá, Colombia ARTICLE INFO Keywords: Structure-live load interaction Live load as seismic weight Base-isolated storage structures ABSTRACT This paper presents the results from finite element models of based-isolated storage buildings subjected to ground motion excitation and supporting rigid blocks with the possibility to slide. Main components of the models were first compared and calibrated with the results from numerical solutions, finite element software, and shake table tests. The successfully verified finite element models were then used to assess ASCE 7–16 design provisions for the treatment of storage loads as seismic weight in base-isolated structures. The analyses included multi-story shear buildings of different heights and three-dimensional buildings of three-stories with both reg- ular and irregular plans under combined horizontal and vertical ground excitation. Alternative low and high friction between the rigid blocks (representing the storage live load) and the floor deck were evaluated in the analyses as well as the effect of light versus heavy storage live loads. Ground excitation consisted of 100 records, covering scenarios that range from low to high seismic risk. The combination of cases included in the parametric study led to thousands of nonlinear time history analyses. Selected engineering design parameters (EDP) to conduct the evaluation consisted of isolator deformation and maximum force demands in the lateral load resting system. Calculated EDPs from the detailed models (accounting for inelastic response of the lateral load resisting system coupled with potential sliding of rigid blocks) were compared with calculated EDPs from simplified models with no blocks but having additional floor mass equal to 25% of the design live load. The latter models represented analysis conditions that ASCE 7–16 minimum provisions would allow in consulting practice. This study demonstrates that using the Standard’s minimum provision can lead to: i) significant underestimations of the deformation demand and thus unconservative designs of base isolators; ii) significant underestimations of design forces, and consequently, improper design of the lateral load resisting elements. In order to address these issues, a simple expression recently developed by the authors to estimate the portion of the design live load as seismic weight was also evaluated. It is shown that using the portion of the live load given by this equation in the simplified models with no blocks but having additional floor mass produce very similar EDPs as those obtained from the detailed models with sliding blocks and thus representing a significant improvement over the existing ASCE 7–16 minimum provisions when applied to base-isolated storage structures. 1. Introduction Section 12.7.2 of ASCE 7–16 [1] establishes a minimum 25% of the floor live load in storage areas as part of the seismic weight (inertia) used to design a structure. To help illustrate the provision, Fig. 1(a) shows a base-isolated shear building characterized by a diagonal mass matrix m [ ] p , lateral stiffness matrix k [ ], and viscous damping matrix c [ ] that support a rigid block of mass m bi at the i th floor to represent the storage live load at that level. Because of the intrinsic complexity of modeling the actual interaction of structure and live load objects in consulting practice, ASCE 7–16 allows to represent the system as shown in Fig. 1(b) where live load objects are removed but floors have a mass equal to + m λm pi bi at the i th floor, where λ may be taken as small as 0.25. In common applications, design engineers may be using such minimum provision under the belief that live loads may not be so sig- nificant or not always be present. However, for commercial/industrial facilities whose primary purpose is storage, the standard-prescribed design live load of 12 kN/m 2 (for heavy storage) can be up to four times greater than the self-weight of a typical metal deck floor system. Fur- thermore, Section 2.3.6 of the standard lists 100% of the design live load in one of the basic combinations with seismic load effects, thus implicitly acknowledging that the entire design live load could be https://doi.org/10.1016/j.engstruct.2020.110843 Received 10 October 2019; Received in revised form 11 May 2020; Accepted 19 May 2020 ⁎ Corresponding author at: Department of Civil and Environmental Engineering, Seattle University, 901 12 th Ave, Seattle, USA. E-mail address: smithjh@seattleu.edu (J. Paul Smith-Pardo). Engineering Structures 218 (2020) 110843 0141-0296/ © 2020 Elsevier Ltd. All rights reserved. T