TECHNICAL MANUAL. ARMATA Punching Reinforcement. Deformed Shear Reinforcement to Reduce Congestion

Transcription

1 TECHNICAL MANUAL ARMATA Punching Reinforcement Deformed Shear Reinforcement to Reduce Congestion Version: PEIKKO GROUP 01/2018

2 ARMATA To prevent punching failure of concrete slabs Allows for a slim fl oor Eliminates column capitals and drop panels above columns Quick and easy installation Flexibility in design and delivery Improves the ductility of slabs Improves bonding conditions in concrete elements thanks to ribs on the studs Design according to ACI for static and seismic loading using Peikko Designer Peikko s ARMATA is primarily used to increase the punching shear resistance of cast-in-situ concrete slabs without increasing the slab s thickness. ARMATA can be used in slab-on-grade foundations and in elevated slabs, such as reinforced concrete slabs or posttensioned slabs. When used in elevated slabs, ARMATA can eliminate the need for dropdown panels or column caps, thus reducing the costs associated with formwork for concrete. Compared to traditional reinforcement systems, ARMATA has the added benefit of quick installation times, leading to reduced labor costs. Moreover, a thinner slab will lead to a lower floor-to-floor height and thereby a reduced building height or the possibility to have an extra floor within the same building footprint. Besides increasing the resistance of the slab, ARMATA punching reinforcement also increases its ductility. ARMATA Rail ARMATA is produced from deformed reinforcement bars. The excellent bonding conditions and mechanical properties of the deformed bars allow for an optimized slab design by reducing the total amount of punching reinforcement. ARMATA rails consist of double-headed ribbed studs attached to a steel flat bar. The type, geometry and dimensions of ARMATA rails may be designed and the resistances of the concrete members reinforced by ARMATA rails may be verified using Peikko Designer in accordance with the requirements of ACI ARMATA Punching Reinforcement

3 Contents About ARMATA 4 1. Product properties Structural behavior Limitations for application Material properties Resistances... 7 Select ARMATA 8 Install ARMATA 16 Revision: 002*

4 About ARMATA 1. Product properties Reinforced concrete slabs are currently one of the most popular structural systems used in residential and commercial buildings, parking garages and many other types of structure. The system usually consists of slabs that are locally supported by columns or walls without a beam system (Figure 1). Such a configuration allows for optimal utilization of the floor area and significant savings with regards to the total height of the building. Figure 1. Flat slab supported on columns and walls. Between supports, the slab is usually designed as a two-way slab to resist bending moments in two orthogonal directions. Near the support area, the bending moments are combined with transverse loads reactions from supports. Such combined loading results in a state of stress that may lead to failure of the slab called punching shear. In most cases, the punching resistance of the slab is limited by the thickness of the concrete slab. Punching shear usually occurs when a concrete cone is separated from the slab, bending reinforcement is pulled away from concrete, and the slab falls down due to gravity (Figure 2). Experience shows that failure by punching is particularly dangerous since it is a brittle phenomenon that occurs suddenly without forewarning signs (extensive deformations, cracks, etc.). Moreover, the failure of one column may impact the adjacent columns and lead to a chain reaction failure of the entire reinforced concrete floor. Figure 2. Failure of a slab by punching. A slab without vertical reinforcement has a very limited resistance against punching failure. This resistance may be increased by placing ARMATA rails in the concrete slab in such a manner that it prevents the concrete cone to develop (Figure 3). Besides increasing the resistance of the slab, ARMATA rails also increase its ductility. ARMATA rails are also used in foundation slabs in a similar manner as in floor slabs. Other applications are also possible: ARMATA rails can be used as shear reinforcement in beams and in walls. Figure 3. Flat slab reinforced with ARMATA rails. 4 ARMATA

5 About ARMATA ARMATA rails consist of double-headed ribbed steel studs welded to a steel flat bar (Figure 4a). The flat bar has no load-bearing function; it only guarantees the correct spacing and positioning of the studs during their installation in concrete as prescribed by ASTM-A1044 (2016a). Figure 4a. Example of an ARMATA rail. Figure 4b. Height and cover of ARMATA studs within the slab. C H C H: height C: cover top and bottom The height of the ARMATA studs depends on the thickness of the slab and concrete cover of the flexural reinforcement of the slab (Figure 4b). The head of the studs is considered to be fully anchored into the concrete so that the maximum tensile resistances of ARMATA studs can be developed. ARMATA studs are available in diameters 3 8, 1 2, 5 8, 3 4 and can be identified by the marking PEIKKO # or PG # and the factory number (Figure 4c). ARMATA studs are produced in height increments of half an inch (0.5 ). Studs with quarter-inch increments will be rounded down to the nearest half-inch increment based on Section of ACI and Chapter 6 of ACI 421.1R-10. For example: long studs will be rounded down to Figure 4c. Marking of ARMATA studs. D - Diameter of the head H - Height of the studs d - Diameter of the shank cross-sectional area of double headed stud Marking at the ends of the studs: PG PEIKKO # # Version: Peikko Group ACI /2018 5

6 About ARMATA 1.1 Structural behavior The static model of a locally supported slab without punching reinforcement is shown in Figures 5 and 6. The external loads of the slab are balanced by a system of concrete struts and ties. The punching resistance of the slab is limited by the tensile strength of the ties. Figure 5. Forces in the slab without ARMATA before failure. Figure 6. Forces in the slab without ARMATA at failure. V Bending cracks V Punching crack H H Tension Compression V Tension Compression V Reinforcing the slab with ARMATA involves replacing the concrete ties with vertical steel reinforcement elements (Figure 7). The tensile force is developed in the shank of the ARMATA studs and anchored into concrete at both ends of the studs by the heads. The diameter and number of steel elements to be placed in the slab has to be determined so that: ARMATA studs adjacent to the loaded area/column have sufficient resistance to prevent the development of a punching cone ARMATA punching reinforcement assembly spreads the load further away from the support Figure 7. V Forces in a slab with ARMATA studs. Tension Compression H Un-reinforced area Reinforced area Compressive stress in concrete V 1.2 Limitations for application The ARMATA studs act as vertical tensile components within the system of internal forces in the slab. They have a limited influence on the resistance of the compressive component of this system (concrete struts). The design and detailing of both ARMATA rails and the slab reinforced by ARMATA rails is performed on a case-by-case basis for each project and approved by the Engineer of Record. A comprehensive set of rules for the verification of the resistance of slabs reinforced by rail elements under static and seismic loads is provided by ACI ARMATA

7 About ARMATA 1.3 Material properties ARMATA studs are fabricated in accordance with ASTM-A1044 (2016a). The strength and ductility requirements are: Tensile strength, min 80,000 psi [550 MPa] Yield strength, min 60,000 psi [420 MPa] Elongation in 8, min 14% (ARMATA 3/8, 1/2, 5/8, 3/4 ) 2. Resistances The resistance of a concrete member reinforced by ARMATA rails must be verified case-by-case for each project. Peikko s design software (Peikko Designer ) is available online and can be used to design the ARMATA rail type and size, and to verify the resistances of the concrete members reinforced by the ARMATA rails in accordance with ACI Version: Peikko Group ACI /2018 7

8 Select ARMATA Select ARMATA An example of the procedure used for the design and selection of ARMATA in accordance with ACI created and implemented in Peikko Designer is presented below. Column dimension a = 15in. b = 15in. Concrete strength f c = 5500 psi Concrete density Normal Slab thickness h = 13in. Concrete cover bottom c b = 1in. Concrete cover top c t = 1in. Diameter of bending d bx = No. 4 reinforcement d by = No. 4 Applied load V u = 450 kips Bending moments M uox = 20.0 kip-ft M uoy = 20.0 kip-ft Position of column Internal column h C t C b d by Bending reinforcement d bx d x d y 1. Effective depth of slab» Effective depth d h c d / 2 11 in. y t by x t by bx 3 4 d hc d d / 2 11 in. d d 1 4 x y d in Critical section (b 0 ) and Area of critical section (A c ) (ACI ) c 0 b0 2 a d b d 106 in. A b d in. ² 3. Geometrical characteristics of critical section» Centroid of critical section x y 0 0 l x,i y,i r y,i i lx,i l r l i 0in. 0 in. 0.5d b 0.5d x l x 0.5d a 0.5d y Column b 0 l y» Neutral axis properties Moment of inertia J x d lx,ir i² in. J y d ly,ir i² in. J 4 0in. xy » Principal axis properties Moment of inertia J in. J in.» Rotation of principal axis ARMATA

9 Select ARMATA 4. Design value of punching shear stresses (ACI )» Moment coefficients 1 1 v,x v,y ly 2 lx l 3 l x y» Moments with eccentricity M M cos M sin 25 kip-ft u1 ux uy M M sin M cos 20 kip-ft u2 ux uy» Shear stress at critical section Vu 10 v1m u i v2m u i vu,i psi A J J c Resistance of slab without punching reinforcement at critical section (ACI )» Nominal shear strength for the two-way members without shear reinforcement 4 2 f' c d 4 f' c s vc min 2 f ' c psi b0» Maximum shear strength for the two-way members 8 f ' c psi λ depends on density of concrete β depends on shape of column α s depends on position of column 6. Load bearing capacity of the slab v v 8 f' n u c [psi] ARMATA punching reinforcement can be used. No ARMATA punching reinforcement is needed if: v n v u ARMATA punching reinforcement can be used if: v v 8 f' n u c Maximum resistance of slab exceeded if: v 8 f' u c Version: Peikko Group ACI /2018 9

10 Select ARMATA 7. Dimension of stud (ACI )» Height of studs ARMATA studs are produced in height increments of half an inch (1 2 ). Studs with quarter-inch increments will be rounded down to the nearest half-inch increment based on Section of ACI and Chapter 6 of ACI 421.1R-10. For example: 83 4 long studs will be rounded down to Support s 0 s h hd cu co 11"» Spacing between elements s 5 " s 5 " 3 4» Check spacing Conditions: s 5 s / d Correct s 5 s / d Correct s d IF : v 6 f ' c s 0.75d u IF : v 6 f ' c s 0.5d u (ACI Table ) 8. Outer critical section b1 (ACI )» Nominal shear strength for the two-way members at the outer critical section v v n c,out vc,out 2 f' c b1 Length of outer critical section 2 f ' c v u,out( b 1 ) iterationac,out Area of outer critical section c1 Dimension from column to outer critical section b in. 2 A in. c,out 10 ARMATA

11 Select ARMATA 9. Geometrical characteristics of outer critical section» Centroid of critical section lx,i ri x0 0 in. l y 0 l y,i l x,i r y,i i 0 in. x b 0 y a b b 1 c=d/2 c 1» Neutral axis properties Moment of inertia J x,prov d lx,i ri 7.653x10 in. J y,prov d ly,i ri 7.653x10 in. 4 J 0in. xy,prov » Principal axis properties Moment of inertia J in. 1,prov 6 4 J 2,prov in. 6 4» Rotation of principal axis Design value of punching shear stresses at outer critical section» Shear stress at critical section Vu 10 v1 u1,prov i v2 u2,prov i u,out Ac,out J1,prov J2,prov v M M psi 11. Resistance of slab with punching reinforcement at outer critical section v u v n v v v 2 f' n c,out c,out c v 2 f' u,out [ psi ] c 12. Number of ARMATA studs between column and outer perimeter 1 0 nreq 19 c 0.5d s s Version: Peikko Group ACI /

12 Select ARMATA 13. Number of ARMATA Rails around column 1. Strength condition m c,req g y v v v u s c c c v 3 f' vs b0 s mreq f A yt A 2. Spacing condition - m spac Spacing must fulfill conditions acc. ACI gx 2d g 2d y Total number of Rails around column m req m max 8 m spac A A - The cross section area of one stud s - Spacing between adjacent studs b 0 - Length of critical control perimeter f yt - Specified yield strength of the ARMATA Stud a b g x 14. Resistance of slab with ARMATA at critical section v s,prov c,prov Av f b s 0 n,prov c,prov s,prov yt c psi v 3 f ' psi v v v psi A v the cross-sectional area of the shear reinforcement on one peripheral line parallel to the perimeter of the column section. v n,prov v u [ psi ] 15. Result» Complete ARMATA Rails 8x ARMATA » Combined ARMATA Rails 8x ARMATA & 8x ARMATA ARMATA

13 Select ARMATA Benefits of ARMATA Traditional headed studs with a smooth surface are produced from steel with yield strength 51,000 psi. Since 2016 the standard specification for steel stud assemblies for shear reinforcement of concrete A1044/A1044M- 16a has also allowed the use of double-headed studs produced from ribbed steel. ARMATA studs fulfill these new requirements for ribbed double-headed studs. Based on the A1044/A1044M-16a, ARMATA studs are produced from ribbed reinforcement, which has higher yield strength (60,000 psi) than traditional smooth studs. The higher strength of the ribbed studs allows the use of fewer studs in the slab compared with a design using smooth studs. The higher performance of the ARMATA ribbed studs can reduce the total number of studs per column by an average of 14%. The benefits of using ARMATA studs can be seen in Table 1. The cases presented, with a slab concrete strength of 5000 psi, are designed either with smooth studs and ARMATA ribbed studs. The comparison shows the reduction in the total number of studs per column when ARMATA ribbed studs are used instead of smooth studs. Table 1. Comparison of the number of smooth studs and ARMATA ribbed studs. Case Thickness of the slab Column Load V Ed M uox M uoy Diameter of the stud Number of smooth studs per column Number of ARMATA studs per column [in] [in] [kips] [kip-ft] [kip-ft] [in] [pcs] [pcs] Version: Peikko Group ACI /

14 Select ARMATA The resulting type and layout of the reinforcement proposed by Peikko Designer is the most economical design. If needed, the diameter of studs and the number of ARMATA rails can be manually modified by the user. The designed ARMATA punching reinforcement assembly will be defined by a unique Peikko item code. The plan and section drawings of the selected ARMATA reinforcement can also be printed by Peikko Designer or exported as DWG files. The printed output of Peikko Designer also includes a summary of input data and static verifications of resistances for each individual case within each project. The list of recommended accessories for the installation of ARMATA is also available in the printed output of Peikko Designer. The ARMATA rail may be provided either as a complete element (with all ARMATA studs welded to one steel shape) or may be assembled on-site from two or more shorter symmetrical ARMATA rails (Figure 8). 14 ARMATA

15 Select ARMATA Figure 8. Complete ARMATA rail and equivalent solution with a combination of shorter ARMATA rails. Peikko : 8x ARMATA Peikko : 8x ARMATA & 8x ARMATA The typical procedure for selecting the appropriate type of ARMATA using Peikko Designer is summarized in the diagram in Figure 9. Figure 9. Procedure to select ARMATA. Materials Geometry Forces Type of ARMATA User input Design of ARMATA Resistance of slab Height of studs Number of studs Diameter of studs Spacing of studs Slab without ARMATA Max. resistance of slab (crushing of concrete) Slab with ARMATA Slab outside of the area reinforced by ARMATA Automatic procedure by Peikko Designer 8xARMATA Number of ARMATA Rails around the column Type of stud Diameter of ARMATA Stud Height of the ARMATA Stud Spacing of studs within the ARMATA Rail element between stud Spacing of studs within the ARMATA Rail element between the column and first stud Number of ARMATA Studs within one rail Version: Peikko Group ACI /

16 Install ARMATA Install ARMATA ARMATA rails are installed in the slab according to the design plans. Each ARMATA rail is identified by a color code located at the end of the rail. The color code is determined by the number of rail configurations for each column for a specific project. Example: SR-1 is red and SR-2 is blue. COLUMN COLOR CODED END Bottom installation: ARMATA rails are placed below the main reinforcement of the slab prior to the installation of the bending reinforcement. In order to achieve a sufficient concrete cover of the headed studs, plastic spacers are mounted onto the ARMATA rails. Spacers are delivered with studrails ARMATA

17 Install ARMATA Top installation: The ARMATA rails are placed on top of the main reinforcement of the slab. All bending reinforcement is installed prior to the ARMATA rails Version: Peikko Group ACI /

18 Notes 18 ARMATA

19 Technical Manual Revisions Version: 1/2018. Revision:002* New cover design for 2018 added. Version: Peikko Group ACI /

20 Resources DESIGN TOOLS Use our powerful software every day to make your work faster, easier and more reliable. Peikko design tools include design software, 3D components for modeling programs, installation instructions, technical manuals and product approvals of Peikko s products. peikko.com/design-tools TECHNICAL SUPPORT Our technical support teams around the world are available to assist you with all of your questions regarding design, installation etc. peikko.com/technical-support APPROVALS Approvals, certificates and documents related to CE-marking (DoP, DoC) can be found on our websites under each products product page. peikko.com/products EPDS AND MANAGEMENT SYSTEM CERTIFICATES Environmental Product Declarations and management system certificates can be found at the quality section of our websites. peikko.com/qehs