Introduction to Decks and Deck Systems

AASHTO- Load and Resistance Factor Design (LRFD) Introduction to Decks and Deck Systems V 1.1 Rev. 12.03.07 Credits The content for this class has been provided by the following PB employees: Ed Skrobacz, P.E. and Walter Hucal, P.E. If you have any questions about the content of this course please contact Ed Skrobacz. If you have any technical difficulties, please contact your IT Help Desk. 1

Download Information As with all of our LRFD courses, you may download a PDF version of this course for your future reference. Click on the ATTACHMENTS link located in the upper right corner of this course window to access the document and save the file to your desktop. Successful Completion After completing the content within the class you will be asked to take a final test to ensure that you mastered the key training objectives. You will need to make a minimum score of 80% to receive credit for passing the class. Successful completion of the class will earn 0.1 IACET CEU. Please refer to your state s specific continuing education requirements regarding applicability. 2

Curriculum This class is the seventh class in the Structures TRC curriculum for LRFD Design, developed internally at PB. The curriculum focuses on the following ten areas of major change introduced by the LRFD Bridge Design Specifications: Introduction to LRFD Loads and Load Factors Concrete Structures Steel Structures Buried Structures Foundations Decks & Deck Systems Joints and Bearings Abutments, Piers, and Walls Railings Class Objectives After completing the course you will be able to identify: 1. What is new or changed in the latest AASHTO LRFD Specification. 2. The three (3) STATIC analysis methods cited within the 2007 ( 4 th Edition ) of the AASHTO LRFD Design Specifications (ENGLISH Edition). 3. Selected code provisions to consider when designing a deck or a deck system. 4. How to complete a simple example for a reinforced concrete deck slab design. 5. Resources and alternate examples available to designers and engineers. This class will review material at an introductory level. The user is cautioned that the covered material is for regular slabs with regular geometry. It is anticipated that the class will take you approximately 90 minutes to complete. 3

Introduction What s New or Changed Code and Commentary side by side Code Commentary Notations have changed, stress f (this change eliminates confusion with σ = standard deviation as used in the calibration resistance factor) and φ has changed from the strength reduction factor to resistance factor. Introduction What s New or Changed LRFD Changes Units have changed from psi to ksi Changes to minimum concrete slab thickness Changes to load factors & load groups Changes to the design live load Changes to live load distribution/methodology New Analysis and Design Methods Lightweight Concrete Provisions New Crack Control Provisions New Guidance on Bar Cutoffs Shear Analysis by Sectional Method (MCFT) 5

Introduction What s New or changed Additional Changes Max & Min Reinforcement requirements have been revised New Resistance Factor Φ based in structural behavior (i.e. strain) There is a new Section 4 which deals with STATIC structural analysis of decks Railing / Overhang design has been revised. (Section 13 and Appendix) New approximate formulas are provided for live load force effects for fully / partially filled grids & unfilled grid decks composite with reinforced concrete deck slabs Class Outline Introduction General Design Considerations Types of Decks Methods of Design Approximate Design Methods Strip Method Deck Overhang Design Empirical Design Method Other Design Methods (Refined Methods) Reinforced CIP Concrete Deck Slab Example using the Strip Method Metal Deck Systems Wood Decks References Conclusion 6

General Design Considerations Design Considerations Material & Weight Cost $$ Time of Construction Type of Formwork Deck Staging & MPT Constructability Long Term Durability Grade & Drainage Location of the Structure Skew Joints CIP Exodermic TM Bridge Deck on Vertical Lift Bridge In New Jersey Exodermic is a trade mark of the DS Brown Company General Design Considerations Specific Considerations identified in LRFD include: Continuity & Composite Construction: Strongly encouraged (Article 9.4.1) Deck Drainage: Provide longitudinal slopes and cross slopes (2.6.6.3., 9.4.2). Design and detailing of deck drainage near deck joints. Avoid scuppers on bridges if possible! Deck Appurtenances: Function to safely direct traffic on a bridge 7

General Design Considerations Edge Supports: Provide at lines of discontinuity (9.4.4) General Design Considerations Stay in Place (SIP) formwork may be used to support the uncured deck. SIP formwork should not be used in the overhang portion of concrete decks. SIP forms are designed to behave elastically. (Article 9.7.4.1). Metal forms are designed to: A) Support the Form & Deck Self Weights B) Support the Deck Reinforcement Steel C) Support the Concrete in the Valleys of the Formwork D) Support a 50 psf Construction Service Load E) Limit Dead Load Deflection from A, B & C above to: L / 180 or ½ in for forms with span lengths up to 10 ft. L / 240 or ¾ in for forms with span lengths above 10 ft. F) Develop flexural stresses due to construction service loads of 0.75 F y OR 0.65 f c OR f r for prestressed concrete form panels. 8

General Design Considerations Reinforced & Prestressed- Precast Decks A. Expedite bridge construction. B. A CIP Pour may be made to seal the joints and tie the panels together. C. The typical panel dimension between joints is greater than 5 ft. D. Depth shall not be less than 7.0 in. Some agencies require a higher deck min. E. Shear Keys may be used to join panels. F. Longitudinal post tensioning shall have a min average prestressing force of 0.25 ksi. General Design Considerations All Four (4) AASHTO Limit States must be considered in deck design: A. The Strength Limit State Meet structural requirements. (usually Strength 1) B. The Service Limit State Meet deflection / crack control criteria. C. The Fatigue Limit State Meet stress range criteria. D. The Extreme Event Limit State Transmit force effects from railing. Note: For other than the deck overhang, concrete decks may be assumed to satisfy the Service, Fatigue and Extreme Events Limit States. ( 9.5.1) 9

Types of Decks Unified Design provisions for Concrete, Metal and Wood Decks are now incorporated into the LRFD Deck Design Specifications within Section 9. Types of Decks Covered in the LRFD Specs Reinforced, Pre-stressed / Pre-Cast Concrete Metal Grid, Orthotropic Steel & Aluminum Corrugated Metal Deck Glued Laminated Wood Stress Laminated Wood Spike Laminated Wood Plank Wood Decks. NOTE: We will focus on Composite Reinforced Concrete decks in this class most common - other deck types will be briefly discussed Class Outline Introduction General Design Considerations Types of Decks Methods of Design Approximate Design Methods Strip Method Deck Overhang Design Empirical Design Method Other Design Methods (Refined Methods) Reinforced CIP Concrete Deck Slab Example using the Strip Method Metal Deck Systems Wood Decks References Conclusion 11

Approximate Methods of Design Strip Method APPROXIMATE DESIGN METHODS Strip Method (4.6.2) Section 4 provides general information and applicability of approximate methods. Provides formulas for calculating the strip widths for various types of decks. Provides information on the distribution of wheel loads, live load force effects and cross sectional frame distributions. Approximate Methods of Design Strip Method Approximate Design Method (The Strip Method) Important items to consider when using this method include: A. The deck is subdivided into theoretical live load design strips that are perpendicular to the supporting structural components. The strips may be interior or edge strips (Notational Edge Beam). The strips may also be longitudinal or transverse. Can be used for all deck types EXCEPT: (Article 4.6.2.1.1) For CIP Concrete deck with SIP Forms TD 1.) Fully filled and partially filled composite grid decks 2.) The top slabs of segmental concrete box girders 12

Approximate Methods of Design Strip Method B. Place truck or tandem on deck to get the maximum effect. The maximum effect is then applied on the corresponding strip width to obtain effects on a unit basis. C. Use the max. positive moment for design in all positive moment regions. D. Use the max. negative moment for design in all negative moment regions. E. May use other design aids for decks containing prefabricated elements. F. For slab type bridges, such as CIP slab or stressed wood deck which are reinforced longitudinally and the span length is more than 15 ft., the provisions of AASHTO section 4.6.2.3 must be applied. G. When the deck spans in the direction of traffic ( parallel ), LL strips shall: < = 40 in. wide for open grids <= 144 in. (12 ft.) for all other decks with multilane loading Approximate Methods of Design Strip Method H. Instead of performing a 3-D FE Analysis & determining strip widths to get the live load moment effects, AASHTO provides a deck slab design table in the Appendix to Chapter 4. The assumptions used to develop this table include: Moments computed using the equivalent strip method Moments apply to concrete slabs / parallel girders Multiple presence factors are included Dynamic load allowance is included Moments are for decks supported on at least 3 girders Table A4-1-maximum live load moments per unit width 13

Approximate Methods of Design Strip Method I. When spacing of support in secondary direction > 1.5 X spacing of support in primary direction one way slab action prevails and all appropriate wheel loads shall be applied in the primary strip direction and distribution reinforcement shall be included in the secondary direction as per article 9.7.3.2.(for Conc. slabs ) as follows: In which: S = the effective span length taken as equal to the effective length specified in article 9.7.2.3 Approximate Methods of Design Strip Method J. If support spacing in secondary direction < 1.5 X primary support spacing then model 2 way slab as a series of intersection strips. The wheel load distribution = stiffness of strip / total stiffness intersecting strips. In which the strip stiffness is computed as : K s = E I s / S I s = Moment of Inertia of the Strip S = Spacing of the Supporting Components K. It is possible to treat strip as a continuous beam or a simply supported beam as required. L. Wheel loads shall be treated as concentrated loads or patch loads of intensity of P / Tire Contact Area ( 20 in. X 10 in. ). 14

Approximate Methods of Design Strip Method M. Interior Strip Widths for Concrete Deck Slabs Or use AASHTO 3.6.1.3.4 For Parallel Strips width < 144in when multiple lanes are being investigated Nomenclature 15

Approximate Methods of Design Deck Overhang Design Deck Overhang Design Cases Also: Vehicular collision forces are as specified in Article 13. Deck overhang resistance > resistance of bridge barrier Approximate Methods of Design Deck Overhang Design Gutter Line 7.3ft Typical Cross Section 16

Approximate Methods of Design Deck Overhang Design Collision Moment Distribution for the first bay design section Approximate Methods of Design Deck Overhang Design Design Case 1 At Inside Face of Barrier A. Compute M u per unit length including the deck & barrier weights and the barrier moment capacity at the base. B. Compute the axial force for unit length in the overhang as the total transverse resistance of the barrier divided by the critical length of the yield line failure pattern plus 2 times the height of the barrier (i.e.): C. Calculate the required reinforcement using LRFD reinforced concrete design methods. 17

Approximate Methods of Design Deck Overhang Design Design Case 1 At Design Section for the Overhang A. Compute M u per unit length including the deck, barrier and future wearing surface and the barrier moment capacity at the base. The barrier moment capacity in the critical length L c is adjusted by distributing on the critical length plus 30 deg end distributions as illustrated in an earlier slide. B. Compute the axial force for unit length in the overhang as the total transverse resistance of the barrier divided by the critical length Lc plus 2 times the height of the barrier plus 30 degree end distributions (i.e., for our simple example): C. Calculate the required reinforcement using LRFD reinforced concrete design methods. Approximate Methods of Design Deck Overhang Design Design Case 1 At Design Section for the First Bay (See Previous Sketch) A. Extract M 1 and M 2 values per unit length for barrier self weights from the deck design. B. Set the value for M 1 due to collision equal to the barrier moment capacity per unit at the base. C. Calculate M 2 per unit length due to collision by similar triangles assuming M 1 / M 2 due to barrier weight = M 1 / M 2 due to collision. Determine M u per unit length at the design section by interpolation or simply assume it to be equal to M 1 due to collision (Conservative). D. Distribute M U due to collision ( the adjusted barrier moment capacity ) in the critical length Lc by the critical length plus 30 degree end distributions. E. Compute M u per unit length including the deck, barrier and future wearing surface weights and the adjusted barrier moment capacity just computed. F. And then : 18

Approximate Methods of Design Deck Overhang Design F. Compute the axial force per unit length in the first bay section as the total transverse resistance of the barrier divided by the critical length of the yield line failure pattern plus 2 times the height of the wall plus 30 degree end distributions (i.e for our simple example). G. Calculate the required reinforcement using LRFD reinforced concrete design methods. Approximate Methods of Design Deck Overhang Design Design Case 2 For concrete barriers, the case of vertical collision force never controls. Design Case 3 At Design Section for the Overhang A. Determine the equivalent strip width as has been illustrated in the previous section. B. Compute the LL & I Moment using a multiple presence factor of 1.2 for one lane loaded, a dynamic load allowance of 0.33 and a wheel load as shown in the previous illustration. This moment shall be distributed on the computed strip width. C. Determine Mu per unit length which includes the deck, barrier and future wearing surface weights already computed in Case 1 and also the newly computed M LLI value. D. Calculate the required reinforcement using LRFD reinforced concrete design methods. 19

Approximate Methods of Design Deck Overhang Design Design Case 3 At Design Section for the First Bay A. Extract the dead and live load moments at this location from the deck slab design. B. Determine the equivalent strip width at the centerline of the fascia girder. C. Compute the Moment per unit length due to live load and dynamic load allowance by dividing the live load effect by the equivalent strip width just determined in the previous step. D. Determine the M U per unit length which includes the deck, barrier and future wearing surface weights already computed in Case 1 and also the newly computed M LLI value. E. Calculate the required reinforcement using LRFD reinforced concrete design methods. Approximate Methods of Design Deck Overhang Design Final Computations After determining the most critical required reinforcement to satisfy all design cases, select the reinforcement. Then, the following final computations will need to be developed: Minimum reinforcement checks and confirmation of the previously assumed resistance factor φ Serviceability ( i.e. crack control) Computation of reinforcement cutoffs and development if required 20

Empirical Design Method Requirements Include: 1. Applies to Concrete Deck Slabs supported by longitudinal components. 2. Design slab depth excludes loss due to grinding, saw cut grooving, or wear. 3. Cross frames / diaphragms must be used at all lines of Support. 4. For decks with Torsionally Stiff superstructure units such as separated box beams, must provide diaphragms between the boxes at 25 ft maximum OR provide supplemental reinforcement over the girder webs to accommodate transverse bending between the boxes. 5. Supporting superstructure components must be made of steel or concrete. 6. Deck must be fully cast in place and water cured. Empirical Design Method Requirements, cont. 7. The deck must generally be of uniform depth. 8. The Effective Length / Design Depth Ratio should be between 6 and18. 9. Core depth not less than 4 in. 10. Effective length shall not exceed 13.5 ft. 11. The minimum slab depth is not less than 7 in. including wearing surface. 12. There is an overhang on each fascia of at least 5 times the depth of the slab OR 3 times the depth of the slab if there is a concrete composite continuous barrier. 13. f c of concrete deck is not less than 4 ksi. 14. Deck is composite with the superstructure with a minimum of 2 shear connectors every 24 in. 22

Empirical Design Method Requirements, cont. 15. Four layers of reinforcement shall be provided. 16. ( 0.27 in 2 / ft ) minimum As for each bottom layer. 17. ( 0.18 in 2 / ft ) minimum As for each top layer. 18. Bar spacing < = 18 in. 19. F y = 60 ksi Min. 20. Straight Bars, Hooks, Lap splices, Mech. couplers allowed. 21. SIP forms are not allowed with Empirical design. 22. For skews > 25 deg, double reinforcement in the end zones. Empirical Design Method Note: Traditional Design Methods include the Approximate and Refined Methods (For the Approx. Method) 23

Other Design Methods (Refined Methods) REFINED METHODS OF ANALYSIS (4.6.3) Any method that satisfies equilibrium & compatibility requirements, uses stress / strain relationships and considers flexural and torsional deformations may be used including: Force and Displacement methods Finite Difference Method Finite Element Method Folded Plate Method Finite Strip Method APPENDIX A4 DECK SLAB DESIGN TABLE For reinforced concrete slabs valid if limitations are satisfied 24

Class Outline Introduction General Design Considerations Types of Decks Methods of Design Approximate Design Methods Strip Method Deck Overhang Design Empirical Design Method Other Design Methods (Refined Methods) Reinforced CIP Concrete Deck Slab Example using the Strip Method Metal Deck Systems Wood Decks References Conclusion Reinforced CIP Concrete Deck Slab Example using the Strip Method Example Bridge Deck Design Problem Using the Strip Method Problem Information: Superstructure Type: R.C. Deck w/multi-span continuous Composite Steel Girders Width: 46-10½ total, 44-0 gutter to gutter Appurtenance: Type F Parapets Skew: No Skew Girder Spacing : 5-100 Long, 48in deep Simple Span Steel Girders @ 9-9 center to center Rebar Cover : Top cover = 2 ½ in. (5.12.3 includes ½ in. integral wearing surface), Bottom cover = 1 in. (5.12.3 ) Properties: f c = 4ksi, F y = 60ksi, Concrete Density = 145 pcf, 2 ½ in bituminous Future wearing surface = 140 pcf (3.5.1-1) Requirements : Design the Deck using the Strip Method in accordance with the AASHTO LRFD Specifications. 25

Reinforced CIP Concrete Deck Slab Example- Strip Method Typical Section Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 1 Select Deck Slab Design Method Use the Strip Method. Design Step 2 Select Trial Deck Slab Thickness The specifications require that the minimum thickness of a concrete deck, excluding any provisions for grinding, grooving and sacrificial surface should not be less than 7 in. ( 9.7.1.1). Most state Jurisdictions require a minimum deck slab thickness of 8 in. (including a ½ in. integral wearing surface). 26

Reinforced CIP Concrete Deck Slab Example- Strip Method In addition, the overall design may include a check of the total superstructure depth (Table 2.5.2.6.3-1) This rarely controls. (i.e.) 0.032L =.032 x 100 x 12 = 38 in. d girder alone = 48 in. Okay does not control Therefore Select 8.5 in. thick deck slab as an initial thickness Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 3 Select Overhang Thickness Using a deck overhang thickness of approximately ¾ in to 1 in. thicker than the deck thickness has proven to be beneficial in past designs. For this Example, an overhang thickness of 9½ in. (including the ½ in. sacrificial layer) is assumed in the design. Design Step 4 Locate Negative Moment Design Section The distance from CL Girder to design section for negative moment in the deck = 1/4 flange width (4.6.2.1.6) Girder Top Flange Width b f = 12 in. One-fourth of the girder top flange width = 3 in. 27

Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 5 Calculate the Un- Factored Moments Determine Un-Factored DL Moments in accordance with AASHTO Section 3.5 DC 1 = Deck Slab Load = 8½ in + 3/8 in. (145 pcf) / 12 in. /ft. = 107 psf ( Includes concrete in the SIP Forms ) DC 2 = Concrete Barrier load ( Each barrier ) = 520 plf DW = Future Wearing Surface (Table 3.5.1-1) = (2½ in.) / 12 ( 140 pcf) = 29 psf The dead load moments must be computed for the deck slab by either : A 3 Dimensional Finite Element Analysis with DC1, DC2 & DW Analyze as a Continuous Beam with DC1 & DW & M = w L 2 /10 Reinforced CIP Concrete Deck Slab Example- Strip Method Table 1 Un-Factored Dead Load Moments ( K-Ft / Ft ) Table 2 Controlling Dead Load Moments ( K-Ft / Ft ) OR For Example: M DC1 (maximum) = (0.107 klf)(9.75ft ) 2 / 10 = 1.02 k-ft / ft 28

Reinforced CIP Concrete Deck Slab Example- Strip Method Reinforced CIP Concrete Deck Slab Example- Strip Method The controlling live load moments for this example are presented in Table 3. Multiple Presence factors have been included in the values shown in the table but dynamic load allowances have not been included. Table 3 Controlling Live Load Moments Using the values presented in Table 3, the maximum controlling positive moment is 36.76 Kip Ft as shown, which is based on one truck and an m value of 1.20. The maximum controlling negative moment as shown is -29.40 K Ft which is based on two trucks and an m value of 1.00 29

Reinforced CIP Concrete Deck Slab Example- Strip Method The dead load moments in tables 1 & 2 are in units of K ft/ ft while the live load moments in table 3 are in K-ft. Now divide the live load moments by the strip width illustrated below in Figure 1 Figure 1 Equivalent Strip Widths In Figure 1, X represents the distance from the load to the point of support and S represents the spacing of the supporting components, each measured in units of feet. The equivalent strip width is then computed in units of inches. X = 2.50 ft 1.0 ft ( From Curb ) = 1.50 ft & S = 9.75 ft. Reinforced CIP Concrete Deck Slab Example- Strip Method Now let s demonstrate the use of the table in the appendix to section 4 30

Reinforced CIP Concrete Deck Slab Example- Strip Method Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 6 Calculate the Factored Moments Factor and Combine Moments for the Strength 1 Limit State using AASHTO Load Factors. Table 4 Load Factors for the Strength 1 Limit State Therefore, the maximum factored positive moment in bay 2 (0.4 pt) is: M pos = 1.25(0.38 k-ft/ft) +1.25(0.19 k-ft/ft) +1.50(0.09 k-ft/ft) +1.75(6.49 k-ft/ft) = +12.21 k-ft/ft = +146.5 in-k/ft The maximum factored negative moment in bay 1 (0. pt) is: M neg = 1.25(-0.74 k-ft/ft) +1.25(-1.66 k-ft/ft) +1.50(-0.06 k-ft/ft) +1.75(-6.07 k-ft/ft) = -13.72 k-ft/ft = -164.6 in-k/ ft 31

Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 7 Design the Deck for Positive Flexure For our design, lets use # 5 bars and we will use LRFD reinforced concrete design methods to arrive at the following results: d = effective depth (in) = total t bottom cover ½ bar diameter Integral WS = 8 ½ in 1in ½ (0.625in) 0.5in = 6.69 in. a = d - d 2 2 M u / 0.85 Φ b f c = 6.69 in 6.69in 2 2 ( 146.5 in k ) / 0.85 (0.90 ) (12 in )(4ksi) = 0.626 in. Reinforced CIP Concrete Deck Slab Example- Strip Method And then: A s req d = M u / Φ Fy ( d a / 2 ) = 146.5 in k / (0.9) ( 60 ksi) ( 6.69 in 0.313 in ) =.425 in 2 / ft Select #5 @ 6 in spacing => As = 0.61 in 2 / ft (Check Agency Standards ) Determine if section is tension controlled and verify the assumed Φ factor c= As F y / 0.85 f c β 1 = 0.610 in 2 ( 60 ksi ) / [(0.85) (4 ksi) (0.85) (12 in / ft )] = 1.05 in ε t = ε u ( d t c ) / c = 0.003 ( 6.69 in -1.05 in) / 1.05 in =.0161 > 0.005 Tensioned Controlled and Φ =0.90 confirmed. Strain Force 32

Reinforced CIP Concrete Deck Slab Example- Strip Method 0.0161 Reinforced CIP Concrete Deck Slab Example- Strip Method Check Minimum Reinforcement Requirements for Flexure (5.7.3.2) AASHTO requires the Factored Flexural resistance of the section M n to be at least equal to the LESSER of 1.2 times the cracking moment M cr determined on the basis of elastic stress distribution OR 1.33 times the factored moment. Calculation by LRFD Concrete design methods yield: M n = 17.1 k-ft M cr = 7.89 k-ft M n > [1.2 (M cr ) = (1.2 )(7.89 k-ft ) = 9.47 k-ft ] Okay And also: 1.33 (146.5 k-in/ft) / 12 = 16.2 k-ft/ft > 9.47 k-ft/ft Okay Note : maximum reinforcement provisions have been removed from the LRFD code in 2005. (5.7.3.3.1) 33

Reinforced CIP Concrete Deck Slab Example- Strip Method Check AASHTO Crack Control Provisions (Not for Empirical Method ) The crack control provisions are newly updated within the LRFD code and are based upon research done by Frosch (2001). The current LRFD code requirements are as follows: (5.7.3.4) The spacing s of the mild steel reinforcement in the layer closest to the tension face shall satisfy the following equation 8.5in #5@6 in 8 8 8 Bottom Transverse Reinforcement Reinforced CIP Concrete Deck Slab Example- Strip Method The maximum positive service moment is first computed: = 85.8 k-in / ft d c = 1.0in (Table 5.12.3-1) + 0.3125 (radius of # 5 Bar) = 1.3125 in (then by traditional service load methodologies) f s = 23.3 ksi βs = 1 + [ dc / 0.7 (h dc)] = 1+[ 1.3125 in / 0.7 ( 8.5 in 1.3125 in) ] = 1.26 γ e = Exposure Factor => use 1.0 for class 1 [700 γe / βs fs ] 2dc = [700 ( 1.0 ) / 1.26 ( 23.3 ksi )] 2(1.3125 in) = 21.2 in s = 8 in < 21.2 in Okay Section satisfies the AASHTO Crack control provisions in the positive moment region 34

Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 8 Design the Deck for Negative Flexure Repeat the Design Steps used in Step 7 with Negative Moment and select #5 @ 6 in Top Negative Reinforcement. Design Step 9 Select Distribution Reinforcement Distribution Reinforcement is placed in the bottom of the deck and is computed as a percentage (%) of the primary reinforcement for positive moment. (9.7.3.2). For primary reinforcement perpendicular to traffic, the distribution reinforcement is: 220 And: Reinforced CIP Concrete Deck Slab Example- Strip Method 220 0.61.41 Select #5 @ 9in in the bottom of the slab A s = 0.41 in 2 /ft = 0.410 in 2 / ft ok 35

Reinforced CIP Concrete Deck Slab Example- Strip Method For Distribution Reinforcement in the top of the slab use Shrinkage and Temperature Reinforcement in accordance with AASHTO 5.10.8.2. This reinforcement shall be distributed equally on both concrete faces and spaced < 3 t or 18in, whichever is smaller. Select #5 @ 9in at the top of the slab; As = 0.41in 2 /ft > 0.094 in 2 / ft ok Reinforced CIP Concrete Deck Slab Example- Strip Method Design Step 10 Select Reinforcement over the Piers. (6.10.1. 7) The total cross sectional area of the longitudinal reinforcement over the piers should not be less than 1% of the slab cross sectional area. A s top = Select additional #5@9in for the top reinforcement so that the total reinforcement is #5 @ 4½ or As = 0.82in 2 / ft > 0.68in 2 / ft A s Bottom = Already selected #5@9in for the Bottom Reinforcement As = 0. 41in 2 / ft > 0.34in 2 / ft 36

Reinforced CIP Concrete Deck Slab Example- Strip Method #5 @ 9 #5 @ 9 #5 @ 6 8 ½ in #5 @ 6 #5 @ 9 DESIGN SKETCH (Not To Scale) Reinforced CIP Concrete Deck Slab Example- Empirical Method 9 ½ in DESIGN SKETCH (Not To Scale) 37

Metal Deck Systems Metal Grid Decks may be required to satisfy the following Selected LRFD Requirements: Live Load Deflections (2.5.2.6, 9.5.2) Tire Contact Area with Deck (3.6.1.2.5) Approximate & Refined Methods (4.6.2.1,9.8.2.1) Fatigue and Fracture (6.6) Shear Connectors (6.10.10) Metal Deck Systems Orthotropic Decks may be required to satisfy the following selected LRFD Provisions: Live Load Deflections ( 2.5.2.6,9.5.2 ) Wearing Surfaces ( 9.8.3.3 ) Tire Contact Area with Deck ( 3.6.1.2.5 ) Approximate Analysis ( 9.8.3.5 ) Refined Analysis ( 9.8.3.4, Sect 4) Distortion Induced Fatigue (6.6.1.3.3) 39

Metal Deck Systems Corrugated Metal Decks may be required to satisfy the following selected LRFD Provisions: Live Load Deflections (2.5.2.6.2, 9.5.2) Tire Contact Area with Deck (3.6.1.2.5) Composite Action with Deck Pan (9.8.5.3) 40

Wood Decks Wood Decks may be required to satisfy the following: Nominal Deck Thickness ( 9.9.2 ) ( At least 6 inches or 4 inches for plank deck roadways ) Approximate Analysis ( 9.9.3 ) Refined Methods ( 9.9.3 ) Shear Design ( 9.9.3.2 ) Deformation ( 9.9.3.3 ) Wearing Surface ( 9.9.8 ) 42

References Standard plans for Timber Highway Sructures http://www.fpl.fs.fed.us/documnts/pdf1996/lee96b.pdf NHI Course 130081,130081A-130081D Course notes for Load and Resistance Factor design for Highway bridge superstructures Revised April 2007, Michael Baker, Moon Township, PA AASHTO Subcommittee on Bridges and Structures Downloads excellent resource on example LRFD problems http://bridges.transportation.org/?siteid=34&c=downloads Various State DOT Websites LRFD Design Example for Steel Girder Superstructure Bridge, Michael Baker, Moon Township, PA, December 2003 FHWA NHI -04-041 Reinforced Concrete Slab Design Using the Empirical Method by Bridge Sight Solutions for the AASHTO LRFD Bridge Design Specifications Publication No. BSS09011999-1 US Department of Transportation Federal Highway Administration Bridge Technology LRFD Product List a valuable list of available LRFD Resources http://www.fhwa.dot.gov/bridge/lrfd/products.cfm Final Assessment Instructions You are now ready to begin the final assessment. The assessment consists of 10 multiple choice questions. You will need to achieve a minimum score of 80% to receive credit for passing the course. If you score below 80%, please go back and review the content of this course, and then retake the assessment to achieve a passing score. When ready, click the Right arrow below to advance to the assessment. 43

Conclusion Thank you for completing this course. If you received a passing score on the assessment, simply close this window to exit the course. Your score will be recorded on your transcript. If you did not achieve a passing score, please review the content of this course and then retake the assessment to achieve a passing score. You may print a certificate from the My Transcript area of PB University by clicking the cert. icon. If you need a certificate that specifically states the IACET certification and credit hours, please email a request to us at pbu@pbworld.com. 44