MGA Structural Engineers Inc.

Glendale, CO, United States

MGA Structural Engineers Inc.

Glendale, CO, United States

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Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.E.,URS Corporation
Canadian Journal of Civil Engineering | Year: 2012

This paper proposes a simple, relatively new elastic-plastic design method for earthquake resisting frames that enables the engineer to directly control the essential aspects of the future behavior of certain structural forms, through basic statics and imposition of predetermined modes of behavior. The method is particularly applicable to the preliminary design of low to mid-rise buildings where the fundamental period of vibrations dominates the response of the system to seismic loading. The focus of this paper is directed towards simplified but accurate manual design rather than sophisticated structural analysis. The premise of the proposed solution is that the constituent elements of the system can be selected in such a way as to cause both the elastic as well as the plastic drift functions to follow linearly varying straight line profiles during all phases of loading. Frameworks designed by this method act not only as structures of uniform response (UR), i.e., uniform strength and stiffness, where the demand/capacity ratios of its members remain the same, both before and after formation of plastic hinges, but they also result in unique solutions, satisfying the prescribed yield criteria, the boundary support, as well as the of static equilibrium conditions.


Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.E.,URS Corporation
Engineering Structures | Year: 2012

This study was prompted by the need to elaborate on the lateral displacements of steel moment frames at incipient collapse. The paper presents relatively simple solutions for assessing lateral displacements of basic flexural modules, as component parts of high-rise frames, at the onset of plastic failure due to combined gravity, and lateral forces magnified by P-delta effects. These solutions are then utilized in conjunction with plastic collapse load interaction diagrams to develop families of generic displacement interaction curves for different boundary conditions. Effects of plastic hinge offsets on the ultimate performance of moment frames, has been discussed in some detail. The paper presents a number of novel concepts and formulae that have not appeared in the literature before. The results of research leading to the preparation of this article have been summarized in the conclusions. It has been shown how these findings may complement the existing literature on the subject. © 2012 Elsevier Ltd.


Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.E.,URS Corporation
Journal of Structural Engineering (United States) | Year: 2012

Performance control (PC) is the ability to design a structure in such a way as to expect predetermined modes of response at certain stages of loading, extents of damage, and/or drift ratios. The primary purpose of this paper is to complement the existing literature on performance-based plastic design of moment frames. PC is, in fact, a new analytic performance-based elastic-plastic design method for ductile structures under seismic loading. It empowers the engineer to control the design rather than investigate design-related numerical output. Failure mechanisms and stability conditions are enforced rather than tested. Unlike traditional closed-form procedures, PC enables the designer to control the response of the structure at preselected performance stages such as before and at first yield, any fraction of the failure load, or specified drift ratios up to and including incipient collapse. It offers a simple design solution to a rather complex problem. © 2012 American Society of Civil Engineers.


Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.E.,URS Corporation
Journal of Constructional Steel Research | Year: 2012

Plastic Design Analysis (PDA) is a recently developed, case specific procedure that aims at direct displacement based lateral design of steel moment frames. PDA is a byproduct of the classical Plastic Analysis and Design (PAD) method of approach. While PAD can only estimate the ultimate loading at failure, PDA has been developed to address such important design issues as the P-delta effects, sequential hinging and lateral displacements at incipient collapse. This is achieved by, first relating the global stiffness of the sub frames of the structure to the most critical target drift and then providing as much capacity as demand imposed on the elements of the frame. Such schemes embrace envelopes of several initial designs within which member sizes could be rearranged for any purpose while observing the prescribed performance conditions. In the interim, a practical method of forecasting the sequence of formation of the plastic hinges is introduced. PDA, as introduced in this article, is based on several complimentary design concepts and novel formulae that have not appeared in the literature before. © 2012 Elsevier Ltd. All rights reserved.


Grigorian M.,MGA Structural Engineers Inc.
Journal of Bionic Engineering | Year: 2014

Currently, there are only three classical and a handful of emerging design methodologies available to structural engineers worldwide. None of these methodologies can explain the design concepts involved in the realization of natural structures such as trees, nor can they fully address the design needs of contemporary engineering structures. The recently developed Performance Control (PC) incorporates both the essence of the classical concepts and the newer procedures and addresses the observed performance of the structure during its known history of loading. PC attempts to mimic nature by applying the known theories of structures to the design of case-specific frameworks, rather than investigating their results for compliance against prescriptive criteria. Parametric examples have been provided to illustrate the applications of the conceptual design similarities between trees and manmade moment frames. It has been shown that an understanding of the structural performance of trees can enhance the structural design of moment frames, and that bioinspired PC can lead to minimum weight moment frames under lateral loading. The analogous performances of the natural and manmade structures may help explain the structural response of trees to similar loading scenarios. © 2014 Jilin University.


Grigorian M.,MGA Structural Engineers Inc. | Grigorian C.,MGA Structural Engineers Inc.
Structural Design of Tall and Special Buildings | Year: 2016

The purpose of this article is to present a new method of analysis for the structural design of pin-supported rocking wall-moment frames with supplementary devices and post-tensioned stabilizers. The function of the wall is to prevent soft story failure, impose uniform drift and provide support for the supplementary equipment. The proposed methodology lends itself well to several seismic design strategies, ranging from severe damage avoidance, to collapse prevention, to structural self-alignment and repairability. Repairability means avoiding major damage to columns and foundations. The success of the resulting solutions is due to the single degree of freedom behavior of the combined system and the fact that its overall performance is not significantly affected by minor changes in the stiffness of the wall. The sensitivity of the response to wall rigidity is addressed by comparing the maximum elastic slope of the wall with a fraction of the specified uniform drift. The limitations of rocking wall-moment frames, as viable lateral resisting systems, have been addressed. Several worked examples have been presented to provide insight and technical information that may not be readily available from electronic output. The proposed solutions are exact within the bounds of the theoretical assumptions and are ideally suited for manual as well as spreadsheet computations. Copyright © 2015 John Wiley & Sons, Ltd.


Grigorian C.E.,MGA Structural Engineers Inc. | Grigorian M.,MGA Structural Engineers Inc.
Journal of Structural Engineering (United States) | Year: 2016

Rocking-wall moment frames (RWMFs) are unique, lateral resisting structures in which the shear wall pivots about its pinned base rather than act as a fixed base, upright cantilever. The function of the wall is to prevent soft-story failure, reduce drift concentration, and provide suitable supports for energy-dissipating devices. However, despite their favorable seismic performance, their practical design aspects have not been fully addressed in the literature. This paper proposes a new approach based on the principles of design-led analysis. It provides a lucid study of the analytic components and inner workings of RWMFs as efficient lateral resisting systems. While complementing existing literature on the subject, this study presents several interesting findings and useful design conclusions. For instance, it points out that under certain circumstances, neither the rocking wall nor its appendages can influence the ultimate carrying capacity of the frame. The proposed solutions are entirely suitable for manual as well as spreadsheet applications. © 2015 American Society of Civil Engineers.


Grigorian M.,MGA Structural Engineers Inc.
Asian Journal of Civil Engineering | Year: 2013

This paper introduces a number of simple findings that lead to the efficient design of system based earthquake resisting moment frames. A system based design is defined as one that leads to minimum drift and minimum weight solutions, for code recognized seismic frameworks, without resorting to complicated numerical analysis. These findings are used to form an algorithm, which in turn leads to closed form solutions for system-specific performance-based design of earthquake resisting moment frames. The results of some of these findings may be summarized as follows; the efficient design of a representative closed loop sub-frame is one involving beams and columns of equal strength and stiffness, a design may be said to be efficient when the demand/capacity ratios of all of its members are as close to unity as possible, the magnitude of a mid-span concentrated load may be considered small if it is less than half its plastic collapse value acting alone on the same beam.


Grigorian M.,MGA Structural Engineers Inc.
Asian Journal of Civil Engineering | Year: 2014

This article presents a realistic analogy, with practical applications, between green trees and manmade moment frames under similar loading conditions. The paper also introduces a new facet of bioinspiration which attempts to benefit from some of the natural design strategies involved in the structural performance of trees, rather than utilizing them as raw materials. The paper suggests that bioinspiration can help transfer and improve basic design concepts from trees to moment frames under seismic as well as gravity loading scenarios. For instance, it has been shown that earthquake resistant systems can best be realized by performing design led analysis rather than investigating analytic results and that structural design should be performance based rather than instruction oriented computations. In other words, it is preferable for earthquake resistant structures to be designed in accordance with observed rather than expected behavior, i.e., desirable response characteristics should be induced rather than investigated. These features constitute the core of the recently developed performance control (PC) methodology that aims at rational design of engineering structures under both service as well as extreme loading conditions. In the interim a number of new design formulae have also been introduced. Two examples have been provided to demonstrate the applications of the conceptual design similarities between green trees and earthquake resisting moment frames.


Puckett J.A.,University of Wyoming | Erikson R.G.,University of Wyoming | Peiffer J.P.,MGA Structural Engineers Inc.
Journal of Structural Engineering | Year: 2010

Based on in-service inspection of poles with traditional designs, the inventory of Wyoming Department of Transportation (WYDOT) exhibited approximately a one-third cracking rate. A ring-stiffened connection is presently used. Sixteen fatigue tests were performed on 12 ring-stiffened cantilevered traffic signal pole connections to quantify the fatigue resistance. Two pole sizes were tested in three loading configurations: in plane, out of plane, and diagonal. Cyclic loading was applied to produce stress ranges (SRs) at several levels up to 16 ksi in the main member, more than six times the SR observed during monitoring an in-service pole. The WYDOT stiffened connection appears to be adequate to resist Wyoming's sustained winds that average approximately 12 mph in many locations. The possibility of using this connection with longer mast arms exists. Connection bolt fatigue failures were observed and may be the limiting fatigue design feature and important for inspection. © 2010 ASCE.

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