Earthquake Resources

FEMA NEHRP Releases Guidance and Recommendations for the Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories (FEMA P-807-1)

January 2024

One of the issues of significant concern for FEMA’s National Earthquake Hazards Reduction Program (NEHRP) continues to be the risk to the nation presented by older, existing buildings that were constructed prior to the development, adoption, and enforcement of modern building codes. Existing buildings built before modern building codes represent a significant percentage of the nation’s building stock and their often-poor performance in earthquakes poses a significant risk to the resilience of our nation’s communities.

These older, multi-unit wood-frame buildings with brittle, weak, and torsionally irregular stories are often designated as soft, weak, or open-front (SWOF) buildings.  Many were constructed in the 1950s through 1970s and can be found across the United States, especially in California. Besides their structural vulnerabilities, SWOF buildings often house significant numbers of people, including socially vulnerable populations.

The purpose of Guidance and Recommendations for the Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories (FEMA P-807-1) is to advance the understanding of the behavior of SWOF buildings and to encourage improved practice in the design of retrofits. This new report provides technical information about the expected seismic collapse performance of common SWOF building configurations, both in their unretrofitted (or original) and retrofitted conditions. It also presents retrofit design examples. The report is intended to be used by jurisdictions and their consultants to inform decisions regarding ordinance scope and retrofit methods to address this risk from the known earthquake resistance deficiencies in these types of buildings in order to provide additional collapse prevention.

The intended audience for this publication includes building officials, practicing civil and structural engineers, and government officials interested in developing mandatory or voluntary seismic retrofit programs for SWOF buildings.

FEMA originally addressed the risk from SWOF buildings by developing and, in May 2012, publishing Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings with Weak First Stories (FEMA P-807). This guideline introduced a methodology to focus the retrofit on the first story to protect the building from collapse without transmitting excessive additional seismic forces into the upper stories. No change to the FEMA P-807 methodology is deemed necessary based on the work of FEMA P-807-1.

The Applied Technology Council managed the development of FEMA P-807-1.  FEMA also acknowledges its valuable collaboration with the Structural Engineers Association of California to improve awareness among its members about the report.


FEMA NEHRP releases Recommendations for Cordoning Earthquake-Damaged Buildings (FEMA P-2055-2) – a companion publication to Guidance for Accelerated Building Reoccupancy Programs (FEMA P-2055-1) and Post-disaster Building Safety Evaluation Guidance (FEMA P-2055)

January 2024

Post-event building safety evaluations can be one of the most important building code implementation activities for any jurisdiction and its building officials and is the first critical step in its community’s recovery. This was recognized by Section 1241(a) of the Disaster Recovery Reform Act (DRRA). As a result FEMA’s National Earthquake Hazards Reduction Program (NEHRP) has published several resources, including the latest Recommendations for Cordoning Earthquake-Damaged Buildings (FEMA P-2055-2). 

Coordination of building safety evaluations after an event are the responsibility of a jurisdiction’s building officials. They inherently require qualified professionals to make on-the-spot evaluations and decisions regarding continued use and occupancy of damaged buildings. Part of these evaluations is the determination of needed fencing, barricades, or cordons around damaged structures.  These protective measures provide safety against potential collapse or falling debris in an aftershock event or even progressive collapse. However, until now there has been relatively limited technical guidance on how to determine the area to be cordoned.

This new publication provides new recommendations for determining a more streamlined cordon area.  Until now the defacto standard cordoned area has been 1.5 times the height of the building completely around its perimeter.  This publication develops and identifies a collapse shadow area as a wedge of a full circle or limited rectangle based on the potential collapse mode of the building.  This dramatically reduces the cordon and thus reduce the impact of the cordon on recovery.

All buildings that suffer damage sufficient enough to pose a collapse hazard have an inherent “fatal flaw” that was exposed by the earthquake, such as unreinforced masonry, non-ductile concrete, a weak story, or a torsional irregularity. FEMA P-2055-2 relates the observed damage to a building of a given structure type to a potential collapse mode. The report includes damage photos of the various potential collapse modes, and a collapse shadow cordon area is prescribed in accordance with the potential collapse mode in a graphical table.

2055 graph

side by side

This report adds to a series of publications that include Guidance for Accelerated Building Reoccupancy Programs (FEMA P-2055-1) published in Spring 2023 and Post-disaster Building Safety Evaluation GuidanceReport on the Current State of Practice including Recommendations Related to Structural and Nonstructural Safety and Habitability (FEMA P-2055) published in November of 2019.

All three publications highlight activities eligible for several FEMA grant programs including Building Resilient Infrastructure and Communities (BRIC) grant within the Building Code Plus-Up funding “Develop planning, training, and exercises for post-disaster building code enforcement.” For more information about BRIC funding opportunities, please visit:

Learn more about FEMA NEHRP

FEMA is part of the National Earthquake Hazards Reduction Program which leads the federal government’s efforts to reduce the fatalities, injuries and property losses caused by earthquakes.

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Earthquake Safety Checklist (FEMA B-526)

 


 

A Step Forward, recommendations for Improving Seismic Code Development, Content, and Education

April 2022 

FEMA P-2191, A Step Forward, recommendations for Improving Seismic Code Development, Content, and Education  summarizes recommendations to improve seismic code and standard development, content and education.

FEMA P-2191 identifies how improved content, usability and better distribution of updates would improve the public’s understanding of seismic codes.  It also suggests seismic code and standard education to practicing engineers and building officials.

Seismic codes and standards provide necessary regulations for building design and construction to meet the required level of seismic performance.  However, there are many areas where seismic codes and standards can be improved.  This report helps to capture the opinions and recommendations of seismic code and standard developers, users and other stakeholders.

 

 


FEMA Publishes Safety at Home

March 2, 2020

Half of all Americans live in areas subject to earthquake risk, and most Americans will travel to seismically active regions in their lifetime.  FEMA is fostering awareness of earthquake risks in the United States through the newly developed FEMA P-530, Earthquake Safety at Home.

This publication is intended to show readers why earthquakes matter where they live, and how they can “Prepare, Protect, Survive, Respond, Recover and Repair” from an earthquake.  This publication will help readers become familiar with why and where earthquakes might occur.  It discusses wide-ranging steps that readers can take to adequately prepare and protect themselves, their family, and their belongings.  These include: developing family response plans, assembling earthquake disaster supplies, securing heavy objects and furniture, retrofitting a home, and more.

During and immediately after an earthquake, guidelines for action can help keep victims safe.  The Respond section of this publication includes a post-earthquake Home Safety Checklist that can assist users in checking the safety of their home before reoccupying it. 

This publication also provides recommendations for post-earthquake recovery and repair that can help individuals and families resume regular activities as quickly as possible.


Recommended Options for Improving the Built Environment for Post-Earthquake Reoccupancy and Functional Recovery Time

January 1, 2021

This FEMA P-2090/NIST SP-1254 –report provides a set of options in the form of recommendations, tasks, and alternatives for improving the built environment, which have been developed and assessed by the Committee of Experts.  It describes community resilience, defines the concepts of reoccupancy and functional recovery, and explains the relationship among these three ideas.  It explains why reoccupancy and functional recovery concepts are needed, describes a target performance state, and identifies potential cost and benefits associated with implementing enhanced seismic design.

Link to the Report fema_p-2090_nist_sp-1254_functional-recovery_01-01-2021


FEMA Releases Updated Report on Seismic Design of Rigid Wall-Flexible Diaphragm Buildings 

December 2021

FEMA’s National Earthquake Hazards Reduction Program (NEHRP) has released the updated edition of Seismic Design of Rigid Wall-Flexible Diaphragm Buildings. This technical guidance document provides study results, design examples and descriptions for an alternative seismic design method for rigid wall-flexible diaphragm (RWFD) buildings. These buildings, better known as ?big box? buildings, are typically used for warehouses or retail stores and have experienced severe damage or even collapse in recent earthquakes. 

The updated report includes newly available research and numerical studies on bare-steel-deck and wood diaphragms and expands the design examples to include bare-steel-deck diaphragms.  The update also includes changes to the design procedure for consistency with the ASCE/SEI 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures.

The report presents an alternative design procedure for big box one-story buildings with stiff and strong vertical elements paired with flexible roof diaphragms.  The seismic performance of big box buildings is mainly related to the large displacement of flexible roof diaphragms under earthquake ground motions.

The new alternative procedure provides clear understanding of the flexible diaphragm performance that is  not properly reflected in the current traditional seismic design.  It corrects this weakness by offering increased seismic performance for big box buildings.

The target audience for FEMA P-1026 is engineers that design big box buildings.  This report gives design principles that will improve the seismic performance of big box buildings.


FEMA P-2139: Short-Period Building Collapse Performance and Recommendations for Improving Seismic Design

December 30, 2020

FEMA P-2139, Short-Period Building Collapse Performance and Recommendations for Improving Seismic Design, is a four-part technical resource that provides the findings and conclusions related to this paradox.  The document recommends how to improve seismic design for short-period buildings.  It includes documents of a multi-year investigation of the response behavior and collapse performance of different structural systems to identify causes and develop solutions for short-period buildings.

The three studies presented in this series investigate three structural systems: wood light-frame, special reinforced masonry shear wall and steel special concentrically braced frame systems.  Based on the analyses of the select structural systems, the document recommends a new approach to model seismic collapse performance and ways to resolve the paradox.       

The recommendations aim to strengthen short period buildings across the nation by improving design, predicting collapse potential and enhancing building codes.  The four volumes consist of

 


2020 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures

FEMA P-2082 (2020 Edition)

September 2020

FEMA is pleased to announce the release of FEMA P-2082, 2020 National Earthquake Hazards Reduction Program (NEHRP) Recommended Seismic Provisions for New Buildings and Other Structures. The release of the 2020 NEHRP Provisions marks the tenth edition of this widely recognized and reputable technical resource document since its first edition in 1985.

The NEHRP Provisions have been an essential resource for improving national seismic design codes and standards, and construction practices. Changes contained in Parts 1 and 2 of the 2020 NEHRP Provisions are expected to be considered for adoption by ASCE/SEI 7-2022 Minimum Design Loads and Associated Criteria for Buildings and Other Structures, which will be later considered for adoption by the International Building Code 2024.

Consistent with the 2009 and 2015 editions, the 2020 NEHRP Provisions includes two volumes:

Volume 1: Part 1 Provisions and Part 2 Commentary: Part 1 Provisions provides recommended changes to the seismic requirements of ASCE/SEI 7-16, Chapters 11 to 23.  Part 2 Commentary provides a complete commentary for each chapter.  It is comprised of the new commentary to each recommended change contained in Part 1 along with the existing ASCE/SEI 7-16 commentary to unchanged sections.  Listed below are some changes in the 2020 edition

  • Revised intent of the NEHRP Provisions
  • New multiperiod response spectra (MPRS) procedures and related design criteria
  • Three added new site classes
  • Updated risk-targeted maximum considered earthquake (MCER) ground motions based on the most recent 2018 USGS National Seismic Hazard Model, MPRS and updated site classes
  • Design parameters and requirements for coupled shear wall systems
  • Alternative design procedures for rigid wall-flexible diaphragm buildings
  • Updated requirements and limitations for irregularities
  • New seismic design force equations for nonstructural components
  • A concept paper on resilience-based seismic design

Volume 2: Part 3 Resource Papers: Part 3 Resource Papers include 9 individual papers.  They provide background information for some changes in Part 1 and introduce new concepts and procedures for experimental use by the design community, researchers, and standards-development and codes-development organizations. 

For more information about FEMA NEHRP, click here.


FEMA P-2091: A Practical Guide to Soil-Structure Interaction

January 19, 2020

A Practical Guide to Soil-Structure Interaction: Soil-structure interaction (SSI) can make a substantial difference in how buildings behave during an earthquake shaking and how they should be designed.  This Guide is intended to help engineers know when incorporating SSI would be important and to provide examples of how to implement different SSI techniques.  The primary target audience for the Guide is practicing engineers who are familiar with seismic design using ASCE/SEI 7 but who have little to no experience with SSI, and the focus of the Guide is on techniques that practicing engineers can use.

Link to the Guide – https://www.fema.gov/sites/default/files/documents/fema-p-2091-soil-structure-interaction.pdf


Assessing Seismic Performance of Buildings with Configuration Irregularities

September 1, 2018

This guidance evaluates current building code triggers, the influence of structural irregularities on seismic building performance (in terms of collapse probability), and the effectiveness of relevant code provisions.  The objective of the studies conducted under this project was to inform and improve U.S. codes and standards so that structures with configuration irregularities have a level of safety against collapse in an earthquake that is comparable to that for regular structures.  The publication focuses primarily on design requirements for new buildings, with limited consideration of the treatment of irregularities for existing buildings.

With a focus on irregularities that have detrimentally affected structural performance in past earthquakes or that are common in current construction trends, the project considered 12 classes of structural configuration irregularities identified in current U.S. codes and standards and two new classes as follows:

  • Torsional stiffness
  • Reentrant corner
  • Diaphragm discontinuity
  • Out-of-plane offset
  • Nonparallel system
  • Torsional strength
  • Soft story
  • Weight [mass]
  • Vertical geometric
  • In-plane discontinuity
  • Weak story
  • Weak-column/strong-beam

Download Assessing Seismic Performance of Buildings with Configuration Irregularities


Safer, Stronger, Smarter: A Guide to Improving School Natural Hazard Safety

June 2017

Safer Stronger Smarter a Guide to Improving School Natural Hazard Safety equips school safety advocates and stakeholders with the information, tools, and resources they need to promote safer schools in their communities, and the guidebook aims to empower and support decision-makers by providing actionable advice.

FEMA P-1000 can help your community respond effectively and recover quickly from natural disasters.