TAPER THREADED GRIP-TWIST And Position Couplers MECHANICAL SPLICES FOR REINFORCED CONCRETE CONSTRUCTION PROJECTS Technical Data and Performance Review JULY 2003 BarSplice Products, Inc., 4900 Webster Street, Dayton OH 45414, USA Tel: (937) 275-8700 Fax: (937) 275-9566 E-mail: bar@barsplice.com Copyright 2012, Barsplice Products, Inc., "BPI". All rights reserved.
INTRODUCTION and OVERVIEW Creating structural continuity in reinforced concrete structures can be critical. High performance mechanical splices for the reinforcement system are essential in helping safeguard against the catastrophic effects of stress overload. Type 2 performance specifications for mechanical splices have been supplanting traditional requirements for 125 percent of specified yield. Applications include structures that may have to withstand the effects of seismic loading or high wind loading, impact, blast or other dynamic condition. The combination of established and proven swaging technology with Taper Threading and Type 2 seismic performance specifications resulted in the creation of the TAPER THREADED Grip-Twist system. Pre-planned splicing of reinforcing bars is an ideal application for the Taper Threaded Grip-Twist System because couplers can be attached to the bars by the rebar fabricator ahead of shipping to the project site. The self-locating and quick locking nature of the Taper Threaded ends allows for expeditious assembly of the System in the field. When using Taper Threaded Grip-Twist Couplers there is no thread cutting operation to be performed. The threads are already formed and threadprotection is in place. Bar ends may be sheared square, saw-cut, abrasive wheel or even square torch-cut. Bars of different sizes may be connected using Transition Taper Threaded Grip-Twist. For locations where rebars have a bend or offset and cannot be rotated, the Position Taper Threaded Grip-Twist System may be used. 2
MECHANICAL SPLICES and LAP SPLICES There are several technical reasons to avoid lap splices as primary structural elements. Depending upon the application, some or all of the following factors should be considered: 1. When a tensile load is applied to a lapped bar embedded in concrete, a complex stress pattern is generated within the concrete between and around the lapped bar. There is a resulting tendency for the bar to cause splitting of the concrete cover in the plane of the lap, especially under severe loading conditions. 2. Cyclic loading, such as that induced into the reinforcing system during high wind, seismic activity or other dynamic condition, can result in the failure of lap splices. Performance depends upon the quality and compaction of the surrounding concrete. 3. Minimizing structural element size is often an objective of architects and engineers. Building code requirements for lap spices can compromise this objective. The use of lap splices in seismic zones generally is disallowed. 4. Geometric limitations often prevent the use of larger diameter reinforcing bars. Codes prohibit the use of #14 and #18 lap splices. Lap splices cannot withstand inelastic strain excursions because the ensuing destruction of the bond with the concrete will result in the ineffectiveness of the lap. 5. If spalling of concrete cover occurs around the lap bar by fire, corrosion or by another mechanism, the effectiveness of the lap is severely compromised because the performance of a lap is 100% dependent upon the concrete that surrounds it. In these cases, the use of mechanical splices has clear advantages When using reinforcing bars in conjunction with mechanical splices the load transfer between the rebars is independent of the concrete. This is verified by in-air testing. By using mechanical splices, lap bars are eliminated and rebar congestion is minimized. This results in improved space for pouring and vibrating thereby enhancing concrete consolidation, lowering concrete placement costs and improving in-place concrete quality. 3
WELDED JOINTS When considering reinforcing bars for welding applications, ASTM A 706 bars or equivalent must be used to achieve consistent performance. Substitution of other bar materials for welding must be approached with caution; control and identification of the entire heat of reinforcing bars should be exercised. When automated equipment performs welding operations, in-process monitoring systems should record force, temperature, revolutions and other elements of the production process. ACI 318-02 has no provisions for Type 2 performance based welds. Welded rebar joints are not permitted by ACI 318-02 to be used within a distance equal to twice the member depth from the column or beam face or from sections where yielding of the reinforcement is likely to occur as a result of inelastic lateral displacements. When using TAPER THREADED Grip-Twist, there are no bar chemistry restrictions; bars may be ASTM A615 [or equivalent] or ASTM A 706. TAPER THREADED Grip-Twist mechanical splices do not involve welding. All of the quality problems associated with welding are avoided. There are no bar chemistries to establish, no weld qualification procedures to follow, no pre-heat or post-heat requirements, no radiographs to be performed and no risks of burns and accidental fires. In the event that there are requirements to connect reinforcing bars to structural steel, the use of a STRUCTURAL CONNECTOR is recommended. For information on different types of Structural Connectors that are available, including Taper Threaded Grip-Twist Structural Connectors, please contact BarSplice Products, Inc. 4
TYPE 2 TAPER THREADED SPLICES In 1999, Building Code Requirements for Structural Concrete, ACI 318-99, was revised to define two classes of mechanical splice. Mechanical splices that were originally designed to develop 125% x specified yield, in tension or compression, became classified as Type 1 mechanical splices. Under the current definition issued by ACI 318-02 Type 2 mechanical spices shall conform to 12.14.3.2 [Type 1 requirements] and shall develop the specified tensile strength of the spliced bar. The Taper Threaded Grip-Twist system is designed to meet the higher strength requirements defined by ACI 318. INSTALLATION A series of overlapping swaging bites are made to attach male and female prethreaded components to the rebar. The swaging process causes the couplings to deform around the profile of the rebar, thereby positively mechanically interlocking with the rebar deformations. Taper Threaded Grip-Twist does not involve the machining of threads on the rebar itself. Consequently, there is no undercutting of the rebar crosssectional area due to machining and no degrading of the potential strength of the bar. Couplers are code-stamped for identification and traceability. Steel meets the chemistry and grade requirements of ASTM A 108, ASTM A 519 and / or A 576 as applicable. ESSENTIAL ADVANTAGES of the Taper Threaded Grip-Twist System are that parts are COLD-FORGED, NO THREAD-CUTTING REQUIRED, rebars can be LOCALLY sourced, and may be ASTM A615 GRADE 60, GRADE 75 or equivalent. PLUS Rebar congestion and placement problems can be reduced by switching from LAP SPLICES to the Taper Threaded Grip-Twist System. The use of mechanically spliced bars allows for easier fabrication and construction, alleviates reinforcement congestion and eases concrete placement. See Current Data Sheets Issued by Barsplice Products, Inc. for Dimensions and Assembly Data including TRANSITIONS 5
TAPER THREADED GRIP-TWIST DESIGN AND PERFORMANCE Taper Threaded Grip-Twist Couplers do not reduce the cross sectional area of the rebar by a threading operation of the bar; the specified ULTIMATE tensile strength capacity of the bar is maintained at the point of entry into the connecting device. The stress area of engaged taper threads used with Taper Threaded Grip- Twist Couplers is GREATER THAN that of the rebar being connected. Additionally, male threads are ROLLED for HIGH STRENGTH and FATIGUE PERFORMANCE. The added strength of Taper Threaded Grip-Twist is commensurate with the TYPE 2 performance requirements for rebar mechanical splices, which are used in areas subject to the effects of seismic activity. By requiring high performance standards there is a greater level of assurance that structures will perform, as designed, under severe loading conditions. Strength capacities, as demonstrated by in-air test data, are higher than the specified nominal tensile strength of the reinforcing bars to which they are affixed. The strength capacities are higher than the standard commercial ratings of other types of rebar splice devices. Tensile tests by independent laboratories have been performed per ASTM A370 by applying a load to the mechanically spliced rebar. These types of tests clearly show that the Taper Threaded Grip-Twist system resists loads that are more than the specified tensile strength of the reinforcing bars to which they are attached. STRENGTH REQUIREMENTS AND COMPARISON CHART TEST RESULT RANGE TAPER THREADED GRIP-TWIST SPECIFIED YIELD 60,000 PSI LAP SPLICE MAXIMUM 125 % x SPECIFIED YIELD 75,000 PSI TYPE 1 MECHANICAL SPLICE 150 % x SPECIFIED YIELD 90,000 PSI TYPE 2 MECHANICAL SPLICE SPECIFICATION GRADE 60 (A 615) ACI 318-02 See Current Data Sheets Issued by Barsplice Products, Inc. for Test Data and Summaries 6
TAPER THREADED GRIP-TWIST CYCLIC PERFORMANCE A feature of the Taper Threaded Grip-Twist design is the use of rolled external threads, which inherently have high fatigue strength. This feature is important when a structure is subject to the effects of a continuously varying load. Bridges and elevated highways are examples where moving traffic induce varying loads into deck steel and column bars. Containment structures and large reinforced concrete pipes, which are subject to pressure variations, are examples where hoop bars, diagonal and vertical steel is subject to the effects of induced varying load. Tall structures, such as high rise office buildings and towers will likely be subject to wind loading. Cyclic fatigue tests have been performed upon Taper Threaded Grip-Twist Splices in accordance with two different protocols. The first protocol issued by Michigan Department of Transportation is concerned with fatigue in tension. This protocol is a derivative of research findings of NCHRP project 10-35, which was conducted by WJE 1988 through 1991. The second protocol is a longstanding pre-qualification requirement of CalTrans, which was intended to envelope some of the effects of seismic activity. Results for #11 Taper Threaded Grip-Twist splices, are summarized as follows: NUMBER CYCLES N cyc RANGE OF STRESS f f MINIMUM STRESS IN REINFORCING BAR MAXIMUM STRESS IN REINFORCING BAR FRACTURE STRENGTH AFTER FATIGUE FINAL PERCENTAGE OF SPECIFIED YIELD f y 1,000,000 12 ksi +12 ksi +24 ksi 107.6 ksi 179% 1,000,000 18 ksi +6 ksi +24 ksi 107.5 ksi 179% 10,000 50 ksi -25 ksi (Compression) +25 ksi 107.5 ksi 179% For more details on these tests, including force - deformation curves, see report WJE No. 1999.3113. 7
POSITION TAPER THREADED GRIP-TWIST COUPLERS The POSITION Taper Threaded Grip-Twist Coupler device provides a solution for the use of threaded systems where it is impractical or impossible to engage threads by rotating rebars due to a bar-bend or offset. A series of overlapping swaging bites are made to attach pre-threaded and pre-assembled components to the rebar. The swaging process causes the couplings to deform around the profile of the rebar, thereby positively mechanically interlocking with the rebar deformations. The POSITION Taper Threaded Grip-Twist Coupler is a complementary product to the Standard Taper Threaded Grip-Twist Coupler because it is not necessary to rotate the rebar to engage the threads. Instead, a preinstalled threaded stud is rotated. The stud unwinds from a swaged connector on one of the bars into a Standard Taper Threaded Female that has been swaged onto the adjoining bar. POSITION Taper Threaded Grip-Twist Couplers are code-stamped for identification and traceability. Steel meets the chemistry and grade requirements of ASTM A 108, ASTM A 519 and / or A 576 as applicable. The POSITION Taper Threaded Grip-Twist Coupler System does not involve the machining of threads on the rebar itself. Consequently, there is no undercutting of the rebar cross-sectional area due to machining and no degrading of the potential strength of the rebar. ESSENTIAL ADVANTAGES of the POSITION Taper Threaded Grip- Twist Coupler Systems are that parts are COLD-FORGED, NO THREAD-CUTTING REQUIRED, rebars can be LOCALLY sourced and NO REBAR ROTATION IS REQUIRED. See Current Data Sheets Issued by Barsplice Products, Inc. for Dimensions and Assembly Data of the POSITION Taper Threaded Grip-Twist System 8
TAPER THREADED GRIP-TWIST SPLICES Summary of potential benefits: Pre-installed, saves time. Simplify fabrication. Eliminates rebar lap. Reduce congestion. Structural continuity, with load transfer independent of concrete. Ease of bar placement. Save space. Reduced member size. Improve job site safety...decrease protruding bars. Improved space for pouring and vibrating. Enhanced concrete compaction. Minimal detailing, more design flexibility. High strength Type 2. No roughing or thread cutting operation on rebars. No chasers, no oils or cutting fluids. No losses of rebar cross-sectional area, no undercutting. TAPER THREADS and TYPE 2 PERFORMANCE Combined. Self-location, quick assembly. Position Coupler for bent bars. No welding. No heat. No fires or burns. Compatible with A 615 & A 706 bars. No chemistry restrictions. HOW TO SPECIFY Specific: Generic: Rebar mechanical splices shall be the Taper Threaded Grip- Twist System and POSITION Taper Threaded Grip-Twist System manufactured by BarSplice Products, Inc., Dayton, OH. Rebar mechanical splices shall be Type 2 COLD SWAGED with TAPER THREADED ENDS. Where rebars cannot be rotated, mechanical splices shall be 3-piece COLD SWAGED with stud. Parts shall be manufactured to the quality requirements of ISO 9001. While the information contained in this document is believed to be accurate at the time of publication, BPI reserves the right to make changes, design modifications, corrections and other revisions as it sees fit, without notice. All products described herein are supplied in accordance with BPI s standard Terms and conditions of Sale. This document is of a promotional nature only. Aspects of structural design, evaluation of product fitness for use, suitability or similar attributes are the responsibility of others. BarSplice Products, Inc., 4900 Webster Street, Dayton OH 45414, USA Tel: (937) 275-8700 Fax: (937) 275-9566 E-mail: bar@barsplice.com 9