Section 16: Spliced Precast Girders
Anchor: #i1603360Materials
Use Class H (HPC) concrete for girder elements:
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 Precast Elements: Anchor: #PBKVMCNO
 Minimum f_{ci} ́ = 4.0 ksi, Maximum f_{ci} ́ = 6.0 ksi Anchor: #OMQVHSJP
 Minimum f_{c} ́ = 5.0 ksi, Maximum f_{c} ́ = 10.0 ksi Anchor: #YGHEQWJP
 Cast in Place Elements: Anchor: #SSXUIJIR
 Maximum f_{c} ́ = 6.0 ksi
Use Class S concrete for cast in place deck (or Class S (HPC) if deicing chemicals are routinely used at the site):
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 Maximum f_{c} ́ = 4.0 ksi
Use prestressing strand with specified tensile strength, f_{pu} of 270 ksi.
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 Use 0.6 in lowrelaxation strands for pretensioning strands. Anchor: #MUJHXNNT
 Use 0.6 in lowrelaxation strands for posttensioning tendons.
Provide post tension system in accordance with Item 426, “Post Tensioning” of the TxDOT Standard Specifications, with the following exceptions:
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 NonSevere Corrosive Environments: Anchor: #SHNEUHBT
 Galvanized or plastic duct can be used Anchor: #CPFTSXVN
 Meet requirements for Protection Level 1B Anchor: #YHWRLCQR
 Do not use tapesealed connections Anchor: #OQCHKAEP
 Severe Corrosive Environments: Anchor: #HJWYRLWP
 Use plastic duct only Anchor: #CPYXFJQY
 Meet requirements for Protection Level 2
All stressed tendons in the finished structure must be grouted. All tendons that are stressed at the precast yard must be grouted prior to transport.
Anchor: #i1605677Geometric Constraints
The minimum numbers of girders in any roadway width is as follows:
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 ISection: 3 girders. If the span is over a lower roadway and the vertical clearance is less than 20 ft., a minimum of 4 girders are required. Anchor: #WVNDTHUH
 USection: 2 girders.
Structural Analysis
Girder designs should meet the following requirements:
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 Use a web or flange thickness that is a whole number and results in the duct not exceeding 0.54 times the least gross concrete thickness at the duct. Anchor: #CQQOGPXT
 Distribute the weight of one railing to no more than three girders. Anchor: #MVKQEINW
 Haunch concrete placed on top of the girder may be considered when determining composite section properties. Anchor: #CIRQSLKJ
 Composite section properties can be calculated assuming either constant modulus of elasticity for the girders and slab, or transforming the sections based upon their respective modulus. Determine respective modulus in accordance with AASHTO LRFD Bridge Design Specifications, Article 5.4.2.4. Anchor: #TXANFQSF
 Live load distribution can be determined from one of the following methods: Anchor: #XACRRPBU
 Must conform to AASHTO LRFD Bridge Design Specifications, Article 4.6.2.2.2 for flexure moment and Article 4.6.2.2.3 for shear when used in conjunction with a line girder analysis. Anchor: #VCQCGQCP
 As determined by use of the lever rule when the span/girder arrangement is out of the applicable range of Articles 4.6.2.2.2 and 4.6.2.2.3 when used in conjunction with a line girder analysis. Anchor: #LBVQECNW
 As distributed by the model when used in conjunction with a grillage, finite element, or other refined model. The model must capture the effects of the complete unit and transfer loads in an acceptable fashion. Anchor: #DFBLXHVH
 When prestressed concrete deck panels or stayinplace metal forms are allowed, design the girder using the basic slab thickness.
Analysis must consider the effects of the following:
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 Staged construction Anchor: #MNGYBYGV
 Addition and removal of temporary supports Anchor: #GXUCQNON
 Locked in forces Anchor: #ORWGGFLX
 Staged post tensioning Anchor: #CYDWNPRK
 Secondary forces due to post tensioning Anchor: #QMKQDTEO
 Torsion due to horizontally curved alignments Anchor: #SBQETMBG
 Superstructure / Substructure interaction Anchor: #TQQGJKRV
 Temperature variation
Design Criteria
Provide a minimum of two tendons per web.
Use diaphragms at all bearing locations.
Provide a full depth diaphragm at all splice and anchorage locations.
Intermediate diaphragm use is not mandatory.
The precast sections must meet the following requirements for transportation:
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 Prestressed Sections:
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 Factor the selfweight load by 1.33 Anchor: #KXCIABKJ
 Strand stress after seating of chucks is not greater than 0.75 f_{pu} for lowrelaxation strands Anchor: #OUNHFIGB
 Use the concrete release strength (f_{ci} ́)
for the following stress limitations:
Tensile stress < 0.24λ (ksi)
Compressive stress < 0.65 f_{ci} ́ (ksi)
Anchor: #TGIDVQFE  Do not drape pretensioning strands. Debond the strands as needed.
Anchor: #DYBKPREE  NonPrestressed Sections:
 Anchor: #MVMPHTWO
 Factor the selfweight load by 1.33 Anchor: #XNIIEKUA
 Design the section as a reinforced concrete member, subject to the provisions in AASHTO LRFD Bridge Design Specifications, Article 5.6.3. Use the concrete release strength (f_{ci} ́) in place of the concrete final strength (f_{c} ́) Anchor: #FYYPDDPJ
 Limit the stress in the reinforcing steel to 36 ksi
The precast sections must meet the following requirements during construction stages:
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 Factor the selfweight load by 1.0 Anchor: #EJWOVSRR
 Include loads to represent weight of form work for splices and strong backs (if applicable) Anchor: #OAKTUWJO
 Use the final concrete strength (f_{c} ́)
for the following stress limitations:
Tensile stress < 0.24λ (ksi)
Compressive stress < 0.6 f_{c} ́ (ksi)
The girder must meet the following requirements in the final (service) condition.
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 Use associated final concrete strengths (f_{c} ́) for the precast sections and cast in place splices Anchor: #JOLGMUSV
 Use effective prestress force after all short and long term losses. Losses can be determined by hand as outlined in Section 4, Pretensioned Concrete I Beams and I Girders, or by analysis software that has concrete time dependent capabilities to capture the effect of creep and shrinkage. Anchor: #CCMYQBIA
 Compressive stress limitations:
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 Service I Loading < 0.6 f_{c} ́ Anchor: #GSQJYYFX
 Effective Prestressing and Permanent (Dead) Loading < 0.45 f_{c} ́
Anchor: #KMJRROKM  Tensile stress limitations:
 Anchor: #SNSOBEEL
 Service III Loading
NonSevere Corrosive Environment < 0.19λ (ksi) ≤ 0.6ksi
Severe Corrosive Environment < 0.09λ (ksi) ≤ 0.3ksi
Anchor: #NEVKCFVQ  Effective Prestressing and Permanent (Dead) Loading – No tension allowed
Anchor: #UUWDPOUR  Service III Loading
 Principal Tensile stress at Neutral Axis
of Web
Service III Loading < 0.110λ (ksi)
All post tensioning must be done prior to placement of the deck.
The composite deck is not a prestressed element and is not held to the stress limitations listed above.
The deck must meet the following requirements:
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 Design Load includes
effects due to the following:

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 Pouring sequence Anchor: #RFCMENIB
 Superimposed loads applied to composite section of Service III. Exclude the effects of creep and shrinkage of deck concrete.
Anchor: #KWIYAUSX  Longitudinal steel must meet the following
requirements:
 Anchor: #XUKLTPXG
 Tensile stress in deck concrete is less than (0.9)(0.24)λ (ksi), use No. 4 bars at 9in spacing Anchor: #XEOEAKYT
 Tensile stress in deck concrete is greater than (0.9)(0.24)λ (ksi), deck reinforcement must equal or exceed 1% of the gross deck crosssectional area (do not use bars larger than No. 6):
Design shear based upon Strength I Loading for the final condition and in accordance with Article 5.7.3.3 of the AASHTO LRFD Bridge Design Specifications. Use the General Procedure as provided by Article 5.7.3.4.2. Do not use provisions of Appendix B of the AASHTO LRFD Bridge Design Specifications. The effective web width must be reduced by 25% of the outer diameter of the splice coupler.
Design ultimate moment based upon Strength 1 Loading for the final condition.
Refer to Section 4, Pretensioned Concrete I Beams and I Girders for interface shear design of the deck to girder flange interface.
Show predicted slab deflections should be shown on the plans. Compute deflections using the same composite sections (constant modulus for girder and deck, or transformed sections) used in the analysis. Denote on plans the assumed modulus (if constant is used) or the assumed values of f_{c} ́ of the individual elements.
Included in plans the assumed construction sequence that includes the following:
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 Order of construction Anchor: #FAOYQLTG
 Shore tower locations Anchor: #IIIDCXLC
 Shore tower loads Anchor: #AQWTALIV
 Lifting / support points of precast members Anchor: #GKUFLFJV
 Girder elevation points Anchor: #QIABMJGY
 Post tensioning sequence
Require contractor to provide a temporary bracing plan of the girders.
Require contractor to provide shoring and erection plan.
Anchor: #HIHDOWSPDetailing
Provide 2in. clear cover to reinforcing steel for entire cross section. Also, increase top slab clear cover to 2.5 in. in areas of state where deicing agents are frequently used.
Provide a minimum tangent length, dependent on duct size and type, of tendon from the anchorage head before introducing any curvature. Determine minimum radius of curvature for individual duct sizes based on published values from suppliers.
Reference Item 426 “Post Tensioning” in the General Notes for all post tensioning, grouting materials, and construction. Note exceptions if Protection Level 1B is used in the design (galvanized duct allowed)
Provide anchorage zone details per Article 5.9.5.6