design of by-pass slip connectors in cold-formed steel ... · pdf filedesign of by-pass slip...

1Light Gauge Steel Engineers Association TECH NOTE (544) 9/04

TECHNICAL NOTEOn Cold-Formed Steel Construction

Light Gauge Steel Engineers Association • Washington, D.C. 20005 • Toll Free (866) 465-4732 • www.LGSEA.com

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DESIGN OF BY-PASS SLIP CONNECTORS IN

COLD-FORMED STEEL CONSTRUCTION

SUMMARY: Slip connectors allow for vertical movement of studs or supporting structure without imposing

additional axial load on wall studs and other wall elements. This Tech Note covers various types of slip connectors

in bypass and below-structure conditions and gives design examples for some of the most common types. It does

not address the common single or double slip track.

Definitions

Bypass condition – A type of connection involving cold-formed steel framed studs, in which the stud members are continu-

ous vertically along a spandrel edge of a floor or roof, and may or may not be connected at the spandrel for lateral support.

Curtain Wall Assembly – An exterior wall system designed to carry only lateral loads. This type of assembly is typically

not designed to carry gravity loads other than its own self-weight.

Slip connector – A clip, brace, angle, plate or other device that restrains a stud in at least one lateral direction, while

permitting vertical movement.

Slip Track – A cold-formed steel shape consisting of a web with two flanges, without stiffening lips, designed to allow the

vertical movement of studs installed between the legs while restraining out-of-plane stud movement. Slip tracks typically

have longer legs than standard tracks, and often require additional mechanical bracing of the stud members.

Spandrel Beam – a structural member loaded in bending only supporting a floor slab or roof deck on one side only. Beams

typically occur at the outside edge of a floor or roof, or along the edge of a floor opening such as openings for elevators or

stairs. Bypass slip connectors are often connected directly to or adjacent to edge beams.

Spandrel Window – A continuous window condition between floors, usually made with non-vision glass.

Story Drift – The lateral movement of one level of a structure with respect to adjacent levels due to the effects of wind or

seismic or other lateral loads.

of the stud wall framing. For many years, this detail has been

applied successfully for interior partitions with light lateral

loads. However, until recently, there have been few options

for exterior wall and bypass slip connections other than the

common slip track.

Determination of Need for Slip

Connectors: Vertical Movement

Slip connectors are used in conditions where vertical move-

ment of the main structure is anticipated, but axial loading

of the stud could cause adverse effects. These effects may

include, but are not limited to, failure of the connections,

buckling of the studs, overstressing and cracking of wall com-

ponents, and increasing the permeability of roof and wall

systems to air and water.

Sometimes, by anticipating vertical movement and provid-

Introduction

In the design of structures, it is important to define the path of

loads through the structure. When non-structural elements are

installed within the structural envelope, they often end up un-

intentionally carrying axial loads. Beams, slabs and other floor

elements are often designed for relatively long spans between

columns. The unintentional loading of interior non-bearing walls

can reduce the live load capacity of supporting elements. For

interior drywall framing, relatively small axial loads can cause

buckling of the studs and cracking of attached sheathing. Exte-

rior members accidentally loaded can lead to excessive deflec-

tion, buckling and failure of the building envelope.

Gypsum drywall manufacturers have developed a detail to

prevent overloading of interior drywall partitions. This de-

tail, called “perimeter relief,” includes a gap at the top of the

wall and allows a standard runner track to “slip” over the top

Light Gauge Steel Engineers Association2 TECH NOTE (544) 9/04

ing adequate support, systems may be designed

in a manner that eliminates the requirement for

slip connectors. Exterior wall studs quite often

have the capacity to carry large vertical loads

in addition to the lateral loads for which they

are designed. However, when considering these

vertical axial loads, the designer must also con-

sider how these loads will get into the stud (the

bypass or top connection) and also how these

loads will be carried by the foundation below.

The designer must also account for other wall

elements, such as windows and doors, and pro-

vide a means for the vertical loads to bypass

these elements (usually through headers and

jamb studs). The footing or floor below the base

of a stud wall must be capable of carrying addi-

tional loads from non-slip conditions, such as

floor live loads and roof gravity loads.

Where the wall studs extend to the underside of

the structure, it is much easier to justify the

elimination of slip connectors or slip tracks at

the tops of the walls. In bypass conditions, be-

cause of the eccentricity of the load from the

stud centerline, it is usually best to include slip

connectors if the anticipated movement and sub-

sequent load is not small.

Drift Connectors: Permitting

Horizontal Movement in the

Plane of the Wall

When the overall structure experiences lateral

loads, such as from a wind or seismic event, story

drift takes place. This is the differential move-

ment of one floor level, or story, relative to the

adjacent floors above and below. When this move-

ment is parallel to a wall, and the wall is fixed to

the floor planes above and below, the wall is

racked out of shape from a rectangle to a paral-

lelogram. If the wall is designed as a shear wall

as a part of the building’s lateral system, it will

have structural elements to resist this racking.

However, non-loadbearing curtain wall assem-

blies typically are not designed as shear walls,

even though they may experience sizable out of

plane loads. When these walls are not a part of

the building’s lateral system, and the designer

does not want them to contribute unintentional support to the

rest of the structure, they may be isolated with drift slip con-

nectors (Figure 2). If the non-loadbearing wall supports a

heavy exterior cladding such as masonry veneer, isolation of

the wall helps prevent cracking of the veneer and may help

reduce the hazard of falling debris during a lateral load event.

Figure 1

Multi-story Construction: Slip Connection

at Every Other Level

Figure 2

Drift Clip

GA

P1/

2"

W/ #12 SCREWSVERTICAL SLOTS

TYPICAL CONT. TRACKHOLD STUD SHORT W/NO ATTACHMENT TO TRACK

WITH FASTENERS AS REQ'D.HORIZONTAL SLOTS

DRIFT SLIDE CLIP


This isolation also reduces stresses on windows, fixtures,

and other openings in curtain wall systems.

Locations of Slip Connectors

The most common location for a slip connection is at the top

of a wall panel, where it comes to the underside of, or by-

passes, a structural element, such as a floor slab or spandrel

beam. Under load, this upper portion of the structure may

deflect up or down. The connector is designed to allow this

movement, without axially loading the stud. Note that in this

configuration, the only axial load a wall component experi-

ences is the dead load from its own self-weight, and the

weight of any cladding that the wall is supporting.

Slip connectors may be located between individual panels

that bypass a structure. The panel connections shown in Fig-

ures 1, 3 and 4 demonstrate this type of connector: each in-

dividual floor level can move independently of every other

floor level. The panels are two stories tall, and the slip con-

nector is located at a level that is convenient for the installer

and finisher (usually at window sill level). Note that either

the male or female portion of this connection (Figures 3 and

4) may be on top.

It is very rare for a slip connector to be at the bottom of a

wall (Figure 5). In retrofitting existing structures (especially

where multi-level roof systems are involved), when the lower

portion of the roof cannot take the dead load of the wall in

combination with drifting snow, the wall may be clipped to

the upper portion of the structure and be seated inside a se-

ries of slip connectors or a slip track. Constructability of this

type of system is more difficult because the wall studs must

be suspended in place with the proper gap at the bottom be-

fore being connected to the structure above.

Note that this Tech Note addresses under structure, bypass,

and horizontal slip conditions. In the bypass condition, the

stud or panel system is located outside the structure, rather

than underneath floor or roof elements. At a bypass condi-

tion, the slip connector must extend from the structural ele-

ment out to the stud wall system. If there is no slip connec-

Panelized Stacked Wall: Slip

Connection at Every Other Floor

Figure 3

Figure 5

Slip Connection at Base (Not Typical)

Figure 4

Slip Pin

Figure 4

( FIELD INSTALLED )

( ASS'BLY SHOP WELDED

É 5 1/2" x 5 1/2" x 1/4" thk.W/ 13/16"Æ HOLE

IN PLACE )

OVER-SIZED HOLEIN BOTTOM TRACK

É 5 1/2" x 5 1/2" x 1/4" THK.W/ 3/4"Æ x 3 3/16" LONGNELSON STUD

3/4"

JOIN

T

( 4 ) PLACESt

É 5 1/2" x 5 1/2"

PLAN VIEW

SECTION VIEW

( FIELD INSTALLED )

É 5 1/2" x 5 1/2" x 1/4" THK.W/ 3/4"Æ x 3 3/16" LONGNELSON STUD

OVER-SIZED HOLEIN BOTTOM TRACK

( ASS'BLY SHOP WELDED

É 5 1/2" x 5 1/2" x 1/4" thk.W/ 13/16"Æ HOLE

IN PLACE )

É 5 1/2" x 5 1/2"

( 4 ) PLACES


partial ribbon windows around the entire building, this joint

is typically at the top of the windows. With brick or masonry

veneer, there is usually a shelf angle or relief angle at each

floor level carrying the dead load of the veneer. In this case,

the control joint is usually directly below this shelf angle.

When very long windows are not continuous around the

structure, the location of the horizontal control joint is not

always detailed at the same elevation. This can create a

condition where wall segments immediately adjacent to

one another are expected to slip vertically. Currently, there

are no joints available on the market for wall systems to

move in this manner. Therefore, detailing of the slip

Figure 6a

Spandrel conditionFigure 6b

Spandrel condition between windows

Figure 6Building Elevation with Partial Spandrel Windows (full spandrel windows similar)

tion, and the connector is assumed to transfer load from the

vertical movement of the structure into the stud, the connec-

tor must be designed for the moment caused by the point of

application of the load being offset from the centerline of

the stud. If this is the case, and a moment connection is made

between the connector and the stud, the wall stud must also

be designed for this moment.

Continuity of Horizontal Joints in a Structure

In a multi-story structure, there are often horizontal control

joints to separate the cladding materials of an exterior wall

between floors. At a spandrel condition, with continuous or

6B 6A

MOMENT CONNECTION TO RESIST OVERTURNING OF KNEE WALL.

CONTINUOUS WINDOW

FIXED CONNECTIONS

2ND FLOOR

(SIMILAR AT ROOF)

SLIP CONNECTION MAY BE SUPPLIED HERE BY WINDOW MANUFACTURER

2ND FLOOR

(SIMILAR AT ROOF)

FIXED CONNECTIONS

IF IMMEDIATELY ADJACENT TO COLUMN, THIS MAY BE FIXED CONNECTION. AWAY FROM COLUMN, SLIP CONNECTION MAY BE REQUIRED.

MAY BE EITHER STACKED (AS SHOWN) OR CONTINUOUS STUD.

COLD-FORMEDSTEEL KICKER

SPANDREL BEAM

2ND FLOOR

(SIMILAR AT ROOF)FIXED CONNECTIONS

CONTINUOUS WINDOW

SLIP CONNECTION MAY BE SUPPLIED HERE BY WINDOW MANUFACTURER

MOMENT CONNECTION TO RESIST OVERTURNING OF KNEE WALL.

MAY BE EITHER STACKED (AS SHOWN) OR CONTINUOUS STUD.

FIXED CONNECTIONS

2ND FLOOR

(SIMILAR AT ROOF)

SPANDREL BEAM

COLD-FORMEDSTEEL KICKER

IF IMMEDIATELY ADJACENT TO COLUMN, THIS MAY BE FIXED ,CONNECTION. AWAY FROM COLUMN, SLIP CONNECTION MAY BE REQUIRED.


Common Types of Slip Connectors

A. Slotted angle for attachment to vertical face

of structure.

The following details show examples of slip connectors commonly used. Other connector configurations not shown

here are also possible and permissible.

B. Slotted angle for attachment to underside or top

of structure.

C. Mechanical clip or channel formed to fit inside or

over stud, to allow for vertical movement while attach-

ing to vertical face of structure.

D. Mechanical clip that fits around flange and lip or

inside stud, which is attached to top or bottom of the

structure.

E. Angle or clip made up of multiple pieces, where one part of the clip slides with respect to the other part: one

part is anchored or fastened to the structure, and the other part is screwed or welded to the stud.

t PROPRIETARY SLIDE CLIP@ EA. STUD

t

t

EDGE ANGLE(BY OTHERS)

@ EACH STUDSLIDE CLIP97 MIL

P.D.F.'s AS REQ'D.@ EACH CLIP

SLIDE CLIP

TWO-PIECEPROPRIETARY

TOP & BOTTOM#10 SCREWS AS REQ'D,

(BY OTHERS)EDGE ANGLE

P.D.F.'s AS REQ'D.@ EACH CLIP

SLIDE CLIP

1 1/2" x 6" x 68 MILx 0'-5" LONG

W/ #12 SCREWS1 1/2" LONG SLOTS(BY OTHERS)

EDGE ANGLE

@ EACH CLIPP.D.F.'s AS REQ'D.

x 1'-0" LONG SLIDE CLIP1 1/2" x 2 3/4" x 68 MIL

1 1/2" LONG SLOTSW/ #12 SCREWS


connections in this type of wall needs to prevent this type

of adjacent vertical movement.

Testing of Slip Connectors for Capacity

The American Society for Testing and Materials (ASTM)

currently does not have a test protocol specifically for slip

connectors. The Center for Cold Formed Steel Structures

(CCFSS) has developed one possible testing protocol based

upon ASTM standards and the AISI North American Speci-

fication for the Design of Cold Formed Steel Structural Mem-

bers. This test method is published as LGSEA Research

Note “Testing and Establishing Design Values for Slip Clips”

(RN 2-02).

In the CCFSS testing protocol, both strength and service-

ability capacities are considered.

Some or all of the following design items should be consid-

ered when designing slip connectors:

Figure 8

Multi-story Construction: Slip Connection at

Every Level

Figure 7

Multi-Story Construction: Single Member

Full Height

1. In-Plane Movement of Wall

With seismic or high-wind loading of a wall system, wall

components may experience forces along the length of the

wall. The connection at the base to the structure below, as

well as the diaphragm action of the sheathing, is usually

enough to prevent lateral wall movement. However, if slip

connectors at the top of a wall restrain such movement, they

may become loaded during a seismic event. Relative to seis-

mic forces, this load may be calculated based on the wall

weight, and should be considered in design of wall slip con-

nections in high seismic zones.

2. Anticipated Amount of Vertical Movement

Slip connectors are typically designed for live load deflec-

tion only, and possibly some anticipated deflection due to

creep of concrete or wood structures. For roof systems, there

could possibly be some upward deflection due to wind uplift

conditions. Additional downward gravity loads due to snow

accumulation and ponding should be considered. Also, multi-

span or cantilevered floor and roof conditions can deflect

FOOTING MUST BE CAPABLE OF CARRYING DEAD LOAD OF ENTIRE WALL

SLIP CONNECTORS AT EVERY LEVEL (TYPICAL)

"STACK" LOCATION IS USUALLY PLACED JUST ABOVE THE FLOORLINE, TO MAKE IT EASIER FOR ACCESS BY INSTALLERS.

BACK TO BACK TRACK: NO SLIP

INSIDE FINISH MUST PERMIT DIFFERENTIAL MOVEMENT AT THESE LOCATIONS, TYP. EACH FLOOR.

AT BACK-TO-BACK TRACK LOCATIONS, CONTROL JOINTS SHOULD BE INSTALLED IN EXTERIOR FINISH MATERIAL

TYPI

CA

L


Figure 10

Stick Framed Stacked Wall: Slip Connection

at Every Other Floor

upward when adjacent spans are loaded downward.

Standard rational engineering analysis, appropriate to the type

of structure and loading conditions, should be used to calcu-

late the anticipated deflection. Once this is done, a connec-

tor should be selected that has the capacity to accommodate

the anticipated movement. Several of the connectors have a

limited range of movement, based on the length of a slot or

gap in the connector. Note that most manufacturers recom-

mend that the screw or bolt be centered in the slot, which

effectively reduces the allowable movement in any one di-

rection to half the slot length. It is recommended that de-

signers do not specify that connectors be “bottomed out” in

either the top or bottom of a slot, since if the fastener is in-

stalled in the wrong end of the slot, the slip connector will

be completely ineffective.

3. Amount of Lateral Load on the Connector

Based on lateral wind and seismic loads, the connectors must

be capable of carrying the lateral loads from the studs back

to the structure. Not only must the connectors be capable of

carrying the load, but the fasteners used for both the stud

and the structure must be investigated separately. Some slide

clip manufacturers have tested the entire assembly, which

includes their clip, the connection to the structure, and the

connection to the studs. Design tables from the manufac-

turer often give different values for different mil thickness

studs, because the stud itself or the connection at the stud

will fail before the slip connector will. Designers are respon-

sible for ensuring the validity of published data from manu-

facturers, and verifying that the appropriate Ω or φ factors

are used, based on AISI Chapter F design requirements.

4. Control Joints

Walls are typically made up of multiple types of materials.

Where a structural slip connector allows for movement of

the structure with respect to the cold-formed steel system,

additional consideration must be given to movement of the

other wall materials. Locations where this occurs include,

but are not limited to:

• At face of slab edge, where a control joint may be

needed on the exterior finish system.

• At the roof side of a bypass parapet (see Figure 9).

• Below relief angles.

• At the inside face of bypass walls (see Figure 8). At

this location, allowance for movement is typically

not as critical, since movement does not compro-

mise the building envelope and allow for thermal

or moisture penetration.

Stacked Wall Conditions

In tall, multi-story bypass conditions, it is difficult and some-

times impractical to ship and install studs longer than 40 -

45 feet. For one-, two-, and sometimes three-story structures,

a single stud is usually used (Figure 7). Most often, wall

stud systems in taller, multi-story bypass conditions are made

to span two stories, and stud panels above are “stacked” on

top of the lower panels (Figure 8). This configuration has

Figure 9

Parapet Bypass at Roof


This “Technical Note on Cold-Formed Steel Construction” is published by the Light Gauge Steel Engineers Association. The information

provided in this publication shall not constitute any representation or warranty, express or implied, on the part of LGSEA or any individual that

the information is suitable for any general or specific purpose, and should not be used without consulting with a qualified engineer, architect, or

building designer. ANY INDIVIDUAL OR ENTITY MAKING USE OF THE INFORMATION PROVIDED IN THIS PUBLICATION

ASSUMES ALL RISKS AND LIABILITIES ARISING OR RESULTING FROM SUCH USE. LGSEA believes that the information

contained within this publication is in conformance with prevailing engineering standards of practice. However, none of the information provided

in this publication is intended to represent any official position of the LGSEA or to exclude the use and implementation of any other design or

construction technique.

© Copyright 2004 Light Gauge Steel Engineers Association • Washington, D.C. 20005 • Toll Free (866) 465-4732 • www.LGSEA.com

Author of this Technical Note: Don Allen, P.E.

the dead load of the system bear on the strip footing or foun-

dation at the ground wall, and at each floor a slip con-

nection is installed. This slip connection carries only the

lateral load from the stud, and all vertical load is trans-

ferred to the ground below.

Similarly, some projects will have slip connections at every

other floor, and fixed connections at the floor below (Figure

1, page 2). With this configuration, less dead load is trans-

ferred to the foundation at the wall perimeter, and only half

as many slip connectors are required. However, the fixed

connections must be designed for both vertical and lateral

load. At the interface between panels, a connection must be

made that prevents dead loads from the upper panel from

being transferred to the lower panel, yet allows lateral loads

to be transferred. This may be done with a plate and pin

connection, as shown in Figures 3 and 4 (shown on page 3).

Other Conditions

In certain conditions, slip connections are either not func-

tional or not appropriate for the system being designed. Be-

low is a summary of some of these special conditions:

• Very high vertical movement, exceeding the capac-

ity of typical connectors.

• Connections where exterior cladding will not toler-

ate excessive movement of substrate, or detailing

does not include control joints at slip locations.

• Bridging across building expansion joints.

• Anticipated building movements will be very small.

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