Technical Bulletin 1

Special Moment Frame Connections with Sloped Columns

Welded moment connections in special moment frames are more susceptible to fracture when the connections are sloped. DuraFuse Frames connections can accommodate slope without changing the stress states in the critical elements.

Technical Bulletin 1

Technical Bulletin 2

ANSI/AISC 358 Chapter 15 DuraFuse Moment Frame CPRP Review Version

AISC Connection Prequalified Review Panel has recently reviewed an ANSI/AISC 358 Ch. 15 proposal incorporating DuraFuse Frames. The chapter is currently working its way through the consensus process. Check out the latest version embodying the design process of this cutting-edge connection system.

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Technical Bulletin 3

How to Use the DuraFuse Features in RAM Frame

RAM Frame software has the option to model moment frame connections as DuraFuse connections. The software accurately models the elastic stiffness of frames with DuraFuse connections and performs the seismic checks that are pertinent to the members and joints. Detailed connection design that is not required for stiffness calculations or member checks is performed outside of RAM.

Technical Bulletin 3

Technical Bulletin 4

Quantifying Connection Rigidity for DuraFuse Frames

Full-scale experiments were performed to evaluate the stiffness of connections in DuraFuse Frames. Sub-assemblies with beam depths ranging from 20.8 to 37.1 inches were subjected to initial cycles within the elastic range. The connection stiffnesses determined from the experiments were 2.7 to 3.5 times greater than the minimum connection stiffness required in order for the connections to be considered fully rigid (FR). Connections in DuraFuse Frames can be modeled as fully rigid (FR) connections for gravity and seismic loads.

Technical Bulletin 4

Technical Bulletin 5

Backbone Curve for DuraFuse Connections

A general backbone curve for the DuraFuse Frames connection was developed for use in nonlinear analysis. The general backbone curve was derived based on nine experimental specimens subjected to cyclic loading. The backbone curve is defined by eight points calibrated from the test data. This bulletin summarizes the backbone curve, describes its development, and compares the general curve with the experimental data.

Technical Bulletin 5

Technical Bulletin 6

Continuity Plates and the DuraFuse Frames Connection

Continuity plates are used in welded moment connections to transfer forces to the column web and to make the stress distribution at the beam-to-column welds more uniform. The DuraFuse Frames connection has a different load path that does not require standard continuity plates to transfer loads to the column. The cover plates in a DuraFuse Frames connection transmit the beam forces to the column and prevent local column flange deformations.

 Technical Bulletin 6

Technical Bulletin 7

How DuraFuse Frames are Represented in RAM

The software RAM Frame has the option to model moment frame connections as DuraFuse Frames connections. When this option is selected, the joints have stiffness parameters assigned to reflect the stiffness of DuraFuse Frames connections, as determined from analytical methods and experimental testing. The beam-to-column connection is considered to be fully restrained (FR) and the panel zone stiffness is modeled using the scissor method, following procedures recommended in the literature.

Technical Bulletin 7

Technical Bulletin 8

Modeling DuraFuse Frames Connections in ETABS

The software ETABS is sometimes used to model steel moment resisting frames. When DuraFuse Frames are used for the steel moment frame, the joints in the ETABS model should be defined to accurately reflect the behavior of the DuraFuse Frames connections. The beam-to-column connection at each joint is considered to be fully restrained (FR) and the panel zone stiffness is modeled using the scissor method, following procedures recommended in the literature.

Technical Bulletin 8

Technical Bulletin 9

DuraFuse Frames Code Approval IAPMO UES ER 610

Third-party code-approval reports are an important component of regulatory compliance in the construction industry, enabling innovation, problem solving and competitiveness. Their use is widespread in the realm of proprietary connection system and seismic technology, assuring compliance or equivalency with the governing building codes, such as IBC or CBC, or referenced standards, such ANSI/AISC 341 or ANSI/AISC 360. DuraFuse Frames technology is covered by the IAPMO UES ER 610.

 Technical Bulletin 9

Technical Bulletin 10

Difference in Repair Cost for DuraFuse Frames vs. Other Steel Moment Frame Systems

Buildings that are designed with current codes are expected to be damaged during severe earthquakes. FEMA-P58 was developed to quantify expected building losses, based on the characteristics of the building and the seismic hazard. This bulletin summarizes a FEMA-P58 study that was used to compare the difference in expected building repair costs for DuraFuse Frames vs. a traditional steel moment frame system (RBS). DuraFuse Frames reduce structural repair costs by a factor of four, and residual drift demolition losses by a factor of ten.

Technical Bulletin 10

Technical Bulletin 11

Post-Earthquake Evaluation of a Building with DuraFuse Frames

The March 18, 2020, earthquake near Salt Lake City, Utah, caused strong shaking at a site where a DuraFuse Frames building was under construction. The building was the new Student Center for the Salt Lake Community College (SLCC) Jordan Campus. A post-earthquake evaluation of the steel frame confirmed perfect performance of the DuraFuse Frames DF360 system during the event, with no damage to the steel frames. DuraFuse Frames systems are the most resilient steel moment frames available.

Technical Bulletin 11

Technical Bulletin 12

Subassembly Stiffness Comparison for R=3 Steel Moment Frames

In low-seismic regions, proprietary moment frame connections may be used for R=3 steel moment frames to reduce beam and column sizes. A study was performed to compare the weight and stiffness of moment frames with R=3 DuraFuse Frames (DFF) and R=3 SidePlate (SP) connections. Finite element modeling of four subassemblies with each type of connection was performed with ANSYS. The analyses showed that the DFF subassemblies had greater stiffness and less connection weight than comparable SP subassemblies. For R=3 moment frames, DFF connections can be used in place of SP connections without changing beam and column sizes.

Technical Bulletin 12

Technical Bulletin 13

DuraCore Combined System for Optimum Building Design

While most steel buildings in high seismic areas use either buckling-restrained braced frames (BRBFs) or special moment frames (SMFs), there are advantages to using combined systems in some cases. DuraCore (DuraFuse + CoreBrace) combines the best features of SMFs and BRBFs. DuraCore can reduce weights, as compared to SMFs, and can improve architectural flexibility and foundation demands as compared to BRBFs. DuraFuse engineers can help EORs explore possible benefits of a combined system on particular projects.

Technical Bulletin 13

Technical Bulletin 14

Using DuraFuse Frames in Seismic Retrofit Applications

Most existing special moment frames do not meet current code requirements. The DuraFuse Frames (DFF) Arrow retrofit introduces a fuse plate that mitigates common deficiencies including welds that are susceptible to brittle fracture, weak column panel zones, insufficient column flexural strength, insufficient frame stiffness, and insufficient beam width-thickness ratio.

Technical Bulletin 14

Technical Bulletin 15

Reducing Seismic Losses by Using DuraFuse Frames

Buildings that are designed with current codes are expected to be damaged during severe earthquakes. SP3 software was used to perform FEMA-P58 analyses to compare expected losses for DuraFuse Frames vs. other special moment frames.

Technical Bulletin 15

Technical Bulletin 16

Using BRBFs with Eccentric Configurations in Combination with DuraFuse Frames

One application of BRBFs that has been underappreciated is their use in eccentric configurations (BRBF-Es). Case studies were performed to compare the weight of BRBF-Es with SMFs in 1-and 3-story frames. BRBF-Es provided nearly the same amount of unobstructed bay space as SMFs with weight reductions of up to 58%. Another case study illustrates how some bays in an SMF can be converted to a BRBF-E, resulting in over 40% reduction in weight and elimination of grade beams without any architectural impact.

Technical Bulletin 16

Technical Bulletin 17

Stiffness of Panel Zones with Cover Plates

In steel moment frames, panel zone flexibility contributes to story drift, so cover plates are often used to stiffen the panel zones. Detailed finite element models were used to evaluate the effectiveness and efficiency of different styles of cover plates. The finite element analyses found that standard cover plates, as used in DuraFuse Frames, provide the same panel zone stiffness as extended cover plates, while requiring less plate weight. When engineers are comparing moment frame systems with cover plates, they should use the same panel zone assumptions regardless of whether standard or extended cover plates are used. When rigid panel zones are assumed for DuraFuse Frames, cover plates will be checked to ensure they meet the requirements for that assumption per ASCE 41 guidance.

Technical Bulletin 17

Technical Bulletin 18

Evaluating the Accuracy of Moment Frame Design Models

Structural models that are used for design must reasonably represent the strength and stiffness of the structure. The accuracy of typical ETABS and RAM models for special moment frame systems was evaluated. For reduced beam section (RBS) and DuraFuse Frames (DFF) systems, ETABS and RAM models produced results that were similar to those obtained from rigorous models where connection geometries were modeled explicitly (using ANSYS). For SidePlate (SP) frames, the ETABS and RAM models based on SP modeling recommendations, had stiffnesses that were more than 1.3 times greater than the upper-bound stiffness determined from rigorous models. The artificial stiffness observed in the SP ETABS and RAM models was caused by inaccurate modeling assumptions recommended by SP. Modeling assumptions for SP frames should be corrected so that SP ETABS and RAM models have reasonably accurate stiffness.

Technical Bulletin 18

Technical Bulletin 19

Beam Lateral Bracing for DuraFuse Frames

Traditional Special Moment Frame (SMF) beams are designed to form plastic hinges under seismic loading. AISC 341-16 specifies prescriptive beam lateral bracing requirements for those beams to mitigate instability caused by the plastic hinges. In contrast, DuraFuse Frames systems have fuse plates that eliminate plastic hinge formation in the beams. DuraFuse Frames systems have been tested without lateral bracing and are prequalified through ER-610 for use without bracing per AISC 341-16 D1.2b and E3.4b. To mitigate lateral torsional buckling unrelated to plastic hinges, DuraFuse Frames systems use beam lateral bracing per AISC 360 based on the maximum moment that can develop in the beam. This prequalified approach results in around 70% fewer beam lateral brace points than other SMF systems, saving time and money on projects. Case studies are presented that illustrate the savings on lateral bracing costs by using DuraFuse Frames.

Technical Bulletin 19

Technical Bulletin 20

Improving Functional Recovery by Using Replaceable Fuses

Current building codes rely on high ductility systems to resist earthquakes safely. Buildings designed in this manner may be impractical to repair following a severe earthquake. Efforts are being made to improve building codes to address re-occupancy and functional recovery. One option is to design more structures as Risk Category IV. This would be costly and may backfire for some systems that already have low periods and are in the acceleration sensitive region of the response spectra. A complimentary or alternative option is to improve the repairability of structures so they can be returned to service after severe earthquakes. Various replaceable fuse concepts have been explored. The most practical concepts are already being used in practice. The most repairable concept for braced frames is BRBFs. The most repairable concept for moment frames is DuraFuse Frames (DFF). FEMA P-58 analysis confirms that DFF moment frames are a cost-effective path to functional recovery.

This technical bulletin summarizes the content from a presentation given by Dr. Richards at the SEAU Continuing Education Conference on March 3, 2021.

Technical Bulletin 20

Technical Bulletin 21

Repair Requirements for Welded and Bolted SMF Connections

For small earthquakes, special moment frames (SMFs) will respond elastically. For moderate and severe earthquakes some amount of inelastic behavior is expected. Welded moment frames are susceptible to damage that is the most difficult to repair. For moderate earthquakes that require repairs, bolted SMFs, including DuraFuse Frames (DFF), might be repaired without replacing any steel. For severe earthquakes, DuraFuse Frames offers better repairability than other SMFs because beam yielding is prevented and the fuse is accessible. Experimental testing has demonstrated that DFF fuses have sufficient energy dissipation capacity to handle multiple, maximum considered events (MCEs). DFF fuses will only require replacement after severe events that result in large residual drifts.

Technical Bulletin 21