G4.1 Scope
Composite partially restrained moment frames (C-PRMF) shall be designed in conformance with this section. This section is applicable to moment frames that consist of structural steel columns and composite beams that are connected with partially restrained (PR) moment connections that satisfy the requirements in Specification Section B3.4b(b).
G4.2 Basis of Design
C-PRMF designed in accordance with these provisions are expected to provide significant inelastic deformation capacity through yielding in the ductile components of the composite PR beam-to-column moment connections. Flexural yielding of columns at the base is permitted. Design of connections of beams to columns shall be based on connection tests that provide the performance required by Section G4.6c and demonstrate this conformance as required by Section G4.6d.
G4.3 Analysis
Connection flexibility and composite beam action shall be accounted for in determining the dynamic characteristics, strength, and drift of C-PRMF.
For purposes of analysis, the stiffness of beams shall be determined with an effective moment of inertia of the composite section.
G4.4 System Requirements
There are no requirements specific to this system.
G4.5 Members
G4.5a Columns
Steel columns shall meet the requirements of Section D1.1 for moderately ductile members.
G4.5b Beams
Composite beams shall be unencased, fully composite, and shall meet the requirements of Section D1.1 for moderately ductile members. A solid slab shall be provided for a distance of 12 in. (300 mm) from the face of the column in the direction of moment transfer.
G4.5c Protected Zones
There are no designated protected zones.
G4.6 Connections
Connections shall be partially restrained (PR) and shall meet the requirements of Section D2 and this section.
User Note: All subsections of Section D2 are relevant for C-PRMF.
G4.6a Demand Critical Welds
The following welds are demand critical welds and shall satisfy the requirements of Sections A3.4b and I2.3:
- (a) Groove welds at column splices
- (b) Welds at the column-to-base plate connections
Exception: Welds need not be considered demand critical when both of the fol- lowing conditions are satisfied.
- (1) Column hinging at, or near, the base plate is precluded by conditions of restraint.
- (2) There is no net tension under load combinations including the overstrength seismic load.
G4.6b Required Strength
The required strength of the beam-to-column PR moment connections shall be determined including the effects of connection flexibility and second-order moments.
G4.6c Beam-to-Column Connections
Beam-to-composite column connections used in the seismic force-resisting system (SFRS) shall meet the following requirements:
- (a) The connection shall be capable of accommodating a connection rotation of at least 0.02 rad.
- (b) The measured flexural resistance of the connection determined at the column face shall increase monotonically to a value of at least 0.5 of the connected beam at a connection rotation of 0.02 rad, where is defined as the moment corresponding to plastic stress distribution over the composite cross section, and shall meet the requirements of Specification Chapter I.
G4.6d Conformance Demonstration
Beam-to-column connections used in the SFRS shall meet the requirements of Section G4.6c by provision of qualifying cyclic test results in accordance with Section K2. Results of at least two cyclic connection tests shall be provided and shall be based on one of the following:
- (a) Tests reported in research literature or documented tests performed for other projects that represent the project conditions, within the limits specified in Section K2
- (b) Tests that are conducted specifically for the project and are representative of project member sizes, material strengths, connection configurations, and matching connection processes, within the limits specified by Section K2
G4.6e Column Splices
Column splices shall meet the requirements of Section G2.6f.