751.11 Bearings - Revision history

Hoskir: /* 751.11.2.4 PTFE (Polytetraflouroethylene) Bearings */

2024-09-11T19:38:10Z

751.11.2.4 PTFE (Polytetraflouroethylene) Bearings

← Older revision		Revision as of 14:38, 11 September 2024
Line 956:		Line 956:
	\|}		\|}
	Note:</br>		Note:</br>
	Vertical pressure = ~~DL<sub>max</sub>~~/A, where A is the total PTFE surface area minus the dimpled area, if applicable.</br>		Vertical pressure = DLmax/A, where A is the total PTFE surface area minus the dimpled area, if applicable.</br>
	Intermediate values may be determined by interpolation. Integer values shall be used for plans reporting.</br>		Intermediate values may be determined by interpolation. Integer values shall be used for plans reporting.</br>
	Dimpled PTFE sliding surfaces are the preferred PTFE type. Flat PTFE may be used with SPM or SLE approval. The contractor is allowed to use unfilled or filled pads so the filled values should be used in design.</br>		Dimpled PTFE sliding surfaces are the preferred PTFE type. Flat PTFE may be used with SPM or SLE approval. The contractor is allowed to use unfilled or filled pads so the filled values should be used in design.</br>
Line 966:		Line 966:
	PTFE dimensions are the same as the bearing pad dimensions.		PTFE dimensions are the same as the bearing pad dimensions.

	Service ~~DL<sub>max</sub>~~ = 50 kips</br>		Service DLmax = 50 kips</br>
	Service LL = 73 kips</br>		Service LL = 73 kips</br>
	PTFE length, L = 11 in</br>		PTFE length, L = 11 in</br>
Line 976:		Line 976:
	Check h<sub>rt</sub> at first-slip:		Check h<sub>rt</sub> at first-slip:

	~~DL<sub>max</sub>~~ /A = 50/100.1= 0.5 ksi = 500 psi</br>		DLmax /A = 50/100.1= 0.5 ksi = 500 psi</br>
	μ = 4%</br>		μ = 4%</br>
	Deflection of bearing pad at first-slip, Δ<sub>s-slip</sub> = ~~ɣFR(μ)DL~~<sub>~~max~~</sub>(h<sub>rt</sub>)/(AG) = 1.0(4/100)50(1.0)/(100.10.2) = 0.1 in</br>		Deflection of bearing pad at first-slip, Δ<sub>s-slip</sub> = ɣ<sub>FR</sub>(μ)DLmax(h<sub>rt</sub>)/(AG) = 1.0(4/100)50(1.0)/(100.10.2) = 0.1 in</br>
	h<sub>rt</sub> ≥ 2Δ<sub>s-slip</sub> = 2*0.1= 0.2 in OK</br>		h<sub>rt</sub> ≥ 2Δ<sub>s-slip</sub> = 2*0.1= 0.2 in OK</br>
	The PTFE sliding surface accommodates the remainder of the thermal movement at the bearing.		The PTFE sliding surface accommodates the remainder of the thermal movement at the bearing.
Line 987:		Line 987:
	This check will be met by satisfying the maximum compressive stress check for the elastomeric bearing pad.		This check will be met by satisfying the maximum compressive stress check for the elastomeric bearing pad.

	~~DL<sub>max</sub>~~/A ≤ 3.0 ksi </br>		DLmax/A ≤ 3.0 ksi </br>
	50/100.1= 0.5 ksi < 3.0 OK		50/100.1= 0.5 ksi < 3.0 OK

	(~~DL<sub>max</sub>~~ + LL)/A ≤ 4.5 ksi </br>		(DLmax + LL)/A ≤ 4.5 ksi </br>
	(50+73)/100.1= 1.23 ksi < 4.5 OK		(50+73)/100.1= 1.23 ksi < 4.5 OK

Hoskir: /* 751.11.2.4 PTFE (Polytetraflouroethylene) Bearings */ fixed text sub formatting errors

2024-09-11T19:09:51Z

751.11.2.4 PTFE (Polytetraflouroethylene) Bearings: fixed text sub formatting errors

← Older revision		Revision as of 14:09, 11 September 2024
Line 921:		Line 921:
	'''General'''		'''General'''

	PTFE bearings shall be used if Δs > 2.5 in.		PTFE bearings shall be used if Δ<sub>s</sub> > 2.5 in.

	PTFE sliding bearing shall consist of a lower unit and an upper unit as follows:		PTFE sliding bearing shall consist of a lower unit and an upper unit as follows:
Line 956:		Line 956:
	\|}		\|}
	Note:</br>		Note:</br>
	Vertical pressure = ~~DLmax~~/A, where A is the total PTFE surface area minus the dimpled area, if applicable.</br>		Vertical pressure = DL<sub>max</sub>/A, where A is the total PTFE surface area minus the dimpled area, if applicable.</br>
	Intermediate values may be determined by interpolation. Integer values shall be used for plans reporting.</br>		Intermediate values may be determined by interpolation. Integer values shall be used for plans reporting.</br>
	Dimpled PTFE sliding surfaces are the preferred PTFE type. Flat PTFE may be used with SPM or SLE approval. The contractor is allowed to use unfilled or filled pads so the filled values should be used in design.</br>		Dimpled PTFE sliding surfaces are the preferred PTFE type. Flat PTFE may be used with SPM or SLE approval. The contractor is allowed to use unfilled or filled pads so the filled values should be used in design.</br>
Line 966:		Line 966:
	PTFE dimensions are the same as the bearing pad dimensions.		PTFE dimensions are the same as the bearing pad dimensions.

	Service ~~DLmax~~ = 50 kips</br>		Service DL<sub>max</sub> = 50 kips</br>
	Service LL = 73 kips</br>		Service LL = 73 kips</br>
	PTFE length, L = 11 in</br>		PTFE length, L = 11 in</br>
	PTFE width, W = 13 in</br>		PTFE width, W = 13 in</br>
	PTFE surface area, A = 143 - (30/100)143 = 100.1 ~~in2~~, assume dimpled area is 30% of total PTFE surface area</br>		PTFE surface area, A = 143 - (30/100)143 = 100.1 in<sup>2</sup>, assume dimpled area is 30% of total PTFE surface area</br>
	Total elastomer thickness, ~~hrt~~ = 1.0 in</br>		Total elastomer thickness, h<sub>rt</sub> = 1.0 in</br>
	Elastomer shear modulus, G = 0.2 ksi		Elastomer shear modulus, G = 0.2 ksi

	Check ~~hrt~~ at first-slip:		Check h<sub>rt</sub> at first-slip:

	~~DLmax~~ /A = 50/100.1= 0.5 ksi = 500 psi</br>		DL<sub>max</sub> /A = 50/100.1= 0.5 ksi = 500 psi</br>
	μ = 4%</br>		μ = 4%</br>
	Deflection of bearing pad at first-slip, Δs-slip = ɣFR(μ)~~DLmax~~(~~hrt~~)/(AG) = 1.0(4/100)50(1.0)/(100.10.2) = 0.1 in</br>		Deflection of bearing pad at first-slip, Δ<sub>s-slip</sub> = ɣFR(μ)DL<sub>max</sub>(h<sub>rt</sub>)/(AG) = 1.0(4/100)50(1.0)/(100.10.2) = 0.1 in</br>
	~~hrt~~ ≥ ~~2Δs~~-slip = 2*0.1= 0.2 in OK</br>		h<sub>rt</sub> ≥ 2Δ<sub>s-slip</sub> = 2*0.1= 0.2 in OK</br>
	The PTFE sliding surface accommodates the remainder of the thermal movement at the bearing.		The PTFE sliding surface accommodates the remainder of the thermal movement at the bearing.

Line 987:		Line 987:
	This check will be met by satisfying the maximum compressive stress check for the elastomeric bearing pad.		This check will be met by satisfying the maximum compressive stress check for the elastomeric bearing pad.

	~~DLmax~~/A ≤ 3.0 ksi </br>		DL<sub>max</sub>/A ≤ 3.0 ksi </br>
	50/100.1= 0.5 ksi < 3.0 OK		50/100.1= 0.5 ksi < 3.0 OK

	(~~DLmax~~ + LL)/A ≤ 4.5 ksi </br>		(DL<sub>max</sub> + LL)/A ≤ 4.5 ksi </br>
	(50+73)/100.1= 1.23 ksi < 4.5 OK		(50+73)/100.1= 1.23 ksi < 4.5 OK

Hoskir: /* 751.11.2.4 PTFE (Polytetraflouroethylene) Bearings */ updated per RR3932

2024-09-10T15:42:29Z

751.11.2.4 PTFE (Polytetraflouroethylene) Bearings: updated per RR3932

@@ Line 920: / Line 920: @@
 '''General'''
 PTFE sliding bearing shall consist of a lower unit and an upper unit as follows:
-The lower unit shall be PTFE bonded to a 1/8” stainless steel plate which is vulcanized to a neoprene pad.
+The lower unit shall be PTFE bonded to a 1/8” stainless steel plate which is vulcanized to a laminated neoprene pad.
 The upper unit shall be a 1/8” highly polished stainless steel plate welded to a steel sole plate.
-Durometer hardness is to be used for sliding bearings.
+Durometer hardness and shear modulus G = 0.2 ksi is to be used for sliding bearings.
-Design:
+The following table represents the coefficients of friction for the design of PTFE sliding surfaces and are to be used instead of LRFD Table 14.7.2.5-1.
-Neoprene Elastomeric Pad
+{| class="wikitable" style="text-align: center;"
-{|
+|+ Design Coefficients of Friction at Various Vertical Pressures
-|Maximum (DL +LL) Compressive Stress ||= 1000 psi
+! rowspan=2 | PTFE Types !! colspan="5" | Coefficient of Friction, μ
 |-
-|Minimum (DL) Compressive Stress|| = 200 psi
+| style="text-align: left" | Filled - Dimpled || 5% || 4% || 4% || 4% || 4%
 |}
 ====751.11.2.5 Multi-Rotational High Load Bearings====

Hoskir: /* 751.11.3.3 PTFE Bearings */ updated per RR3932

2024-09-10T15:39:46Z

751.11.3.3 PTFE Bearings: updated per RR3932

← Older revision		Revision as of 10:39, 10 September 2024
Line 1,235:		Line 1,235:
	'''****''' Designer should verify that minimum dimensions are met or neoprene will melt and flow into the hole during manufacturing of bearing.		'''****''' Designer should verify that minimum dimensions are met or neoprene will melt and flow into the hole during manufacturing of bearing.

			Either stopper plates, or both stopper plates and straps shall be used to restrain potential longitudinal, or longitudinal and transverse pad movement, respectively.

			If anchor bolts are believed to be insufficient in restraining pad transverse movement, straps shall be used if the maximum distance between the anchor bolt and edge of girder is not exceeded. If straps are not required, or do not fit without exceeding this distance, stopper plates shall still be used and without recessed ends.

Hoskir: /* 751.11.3.4 Bearing Edge Distance */ updated per RR3868

2024-07-19T18:53:21Z

751.11.3.4 Bearing Edge Distance: updated per RR3868

← Older revision		Revision as of 13:53, 19 July 2024
Line 1,262:		Line 1,262:
	Heavy loads placed near the edge of a concrete surface can produce spalling. Two precautions should be taken to avoid the problem. Additional reinforcement should be placed under the load and around the corner. The bearing area of the load should not project beyond the straight portion of the stirrups, nor beyond the interior face of a transverse anchor bar (if one is provided). The recommended distance to a step, or the end of the bent cap in the transverse direction is 9 inches.		Heavy loads placed near the edge of a concrete surface can produce spalling. Two precautions should be taken to avoid the problem. Additional reinforcement should be placed under the load and around the corner. The bearing area of the load should not project beyond the straight portion of the stirrups, nor beyond the interior face of a transverse anchor bar (if one is provided). The recommended distance to a step, or the end of the bent cap in the transverse direction is 9 inches.

			Provide minimum support length in accordance with [https://epg.modot.org/forms/general_files/BR/Bridge_Seismic_Design_Flowchart.pdf Bridge Seismic Design Flowchart].

	'''Bearing Clearance'''		'''Bearing Clearance'''

	When beams are placed to end at an intermediate bent, the clearance is governed by the bent up strands, diaphragm reinforcement, skew, and any vertical or horizontal curvature in the profile grade. A 9 inch minimum between bearing pads for ~~prestress~~ is a general rule. For simply supported steel or constant depth girders the recommended minimum clearance is 2 inches between bearing pads. See Dimension "C". Also consider transverse girder offsets when using ~~prestress~~ girders on horizontally curved alignments.		When beams are placed to end at an intermediate bent, the clearance is governed by the bent up strands, diaphragm reinforcement, skew, and any vertical or horizontal curvature in the profile grade. A 9 inch minimum between bearing pads for prestressed girders is a general rule. For simply supported steel or constant depth girders the recommended minimum clearance is 2 inches between bearing pads. See Dimension "C". Also consider transverse girder offsets when using prestressed girders on horizontally curved alignments.

Hoskir: /* 751.11.3.5 Anchor Bolts */ updated per RR3851

2024-03-21T16:57:33Z

751.11.3.5 Anchor Bolts: updated per RR3851

← Older revision		Revision as of 11:57, 21 March 2024
Line 1,320:		Line 1,320:
	{\|		{\|
	\|-		\|-
	\|colspan="4"\|[[Image:751.11.3.5 ~~Part Plan~~.~~jpg\|800px~~\|center]]		\|colspan="4"\|[[Image:751.11.3.5-PartPlan.png\|center]]
	\|-		\|-
	!SQUARE\|\| \|\|style="text-align:center"\|SKEWED\|\|		!SQUARE\|\| \|\|style="text-align:center"\|SKEWED\|\|
Line 1,340:		Line 1,340:

	<center>		<center>
	[[Image:751.11.3.5 ~~Detail Wells and Reinforcement~~.~~jpg\|800px~~\|center]]		[[Image:751.11.3.5-AnchorBoltWell.png\|center]]

	{\| border="1" cellspacing="1" cellpadding="3"		{\| border="1" cellspacing="1" cellpadding="3" style="text-align:center"
	\|-		\|-
	!colspan="7"\|TABLE OF ANCHOR BOLT WELLS		!colspan="8"\|TABLE OF ANCHOR BOLT WELLS
	\|-		\|-
	\|Anchor Bolt Diameter\|\|~~"A"~~ Well Diameter\|\|~~"B"~~ Well Depth\|\|~~"C"~~ Spiral Depth\|\|~~"D"~~ Spiral Diameter\|\|~~Spiral Bar~~ Length\|\|Bolt Extension into Concrete		\|Anchor Bolt Diameter\|\|Well Diameter X\|\|Well Depth Y\|\|Spiral Depth B\|\|Spiral Diameter C\|\|W5 Nominal Length\|\|W5 Actual Length\|\|Bolt Extension into Concrete
	\|-		\|-
	\|1"\|\|3"\|\|12"\|\|9"\|\|~~8 1/~~8"\|\|15'-1"\|\|9"		\|1"\|\|3"\|\|12"\|\|9"\|\|8"\|\|14'-10"\|\|14-'6"\|\|9"
	\|-		\|-
	\|1 1/4"\|\|4"\|\|15"\|\|12"\|\|9 ~~1/8~~"\|\|19’-9"\|\|12"		\|1 1/4"\|\|4"\|\|15"\|\|12"\|\|9"\|\|19’-7"\|\|19'-1"\|\|12"
	\|-		\|-
	\|1 1/2"\|\|4"\|\|18"\|\|15"\|\|9 1/8"\|\|23'-0"\|\|15"		\|1 1/2"\|\|4"\|\|18"\|\|15"\|\|9"\|\|22'-8"\|\|22'-2"\|\|15"
	\|-		\|-
	\|2"\|\|4"\|\|21"\|\|18"\|\|9 ~~1/8~~"\|\|26'-1"\|\|18"		\|2"\|\|4"\|\|21"\|\|18"\|\|9"\|\|25'-9"\|\|25'-2"\|\|18"
	\|-		\|-
	\|2 1/2"\|\|4"\|\|28"\|\|25"\|\|9 1/8"\|\|33'-2"\|\|25"		\|2 1/2"\|\|4"\|\|28"\|\|25"\|\|9"\|\|33'-1"\|\|32'-4"\|\|25"
	\|}		\|}
			Nominal length is based on out-to-out dimension. Actual length is the measured along the centerline of the W5 wire. Both nominal length and actual length includes the length of the three side wires.

	Omit spiral on 21" WF if anchor bolt spacing is less than 6"		Omit spiral on 21" WF if anchor bolt spacing is less than 6".


Line 1,393:		Line 1,394:

	</center>		</center>


	====751.11.3.6 Girder/Beam Chairs====		====751.11.3.6 Girder/Beam Chairs====

Smithk: /* 751.11.3.6 Girder/Beam Chairs */

2022-06-02T15:43:50Z

751.11.3.6 Girder/Beam Chairs

← Older revision		Revision as of 10:43, 2 June 2022
Line 1,453:		Line 1,453:
	</center>		</center>

	The gap and length of plate is variable and dependent on what is required for rebar placement. The details of the ends of closed concrete intermediate diaphragms will need to be modified from the details shown in [[751.22 Prestressed Concrete I Girders#751.22.3.~~8 Open~~ Concrete Intermediate Diaphragms\|EPG 751.22.3.~~8 Open~~ Concrete Intermediate Diaphragms]].		The gap and length of plate is variable and dependent on what is required for rebar placement. The details of the ends of closed concrete intermediate diaphragms will need to be modified from the details shown in [[751.22 Prestressed Concrete I Girders#751.22.3.7 Closed Concrete Intermediate Diaphragms\|EPG 751.22.3.7 Closed Concrete Intermediate Diaphragms]].

	[[Category:751 LRFD Bridge Design Guidelines]]		[[Category:751 LRFD Bridge Design Guidelines]]

Smithk: /* 751.11.3.6 Girder/Beam Chairs */

2022-06-02T15:42:39Z

751.11.3.6 Girder/Beam Chairs

← Older revision		Revision as of 10:42, 2 June 2022
Line 1,416:		Line 1,416:
	</center>		</center>

	~~:'''Detailing Guidance:'''~~		:{\| style="margin: 1em auto 1em auto" align="center"
	~~:See EPG 751.50 ([[751.50 Standard Detailing Notes#A4a3. Miscellaneous\|Notes A4a3.1]] and [[751.50 Standard Detailing Notes#(G1.16)\|G1.16 thru G1.19]]) for appropriate notes to be placed with details.~~		\|colspan="4"\|'''Detailing Guidance:'''
	~~:<font color = "grass">Green</font color = "grass"> items are guidance and shall not be shown on plans.~~
	::{\| style="margin: 1em auto 1em auto" align="~~left~~"
	\|-		\|-
	\|~~<font color~~ = "~~grass~~">(a)~~</font color = "grass">~~\|~~\|3" minimum~~ to ~~beam steps, 9" minimum to end of beam~~.\|\|		\|colspan="4"\|See EPG 751.50 ([[751.50 Standard Detailing Notes#A4a3. Miscellaneous\|Notes A4a3.1]] and [[751.50 Standard Detailing Notes#(G1.16)\|G1.16 thru G1.19]]) for appropriate notes to be placed with details.
	\|-		\|-
	\|~~valign~~="~~top~~"\|<font color = "grass">~~(b)~~</font color = "grass">~~\|\|1/2" minimum~~ and ~~5" maximum. Use beam step if necessary. With a change in girder size, use thicker laminated pads~~ on ~~the tall girder side if necessary~~.~~\|\|width="300"\|~~		\|colspan="4"\|<font color = "grass">Green</font color = "grass"> items are guidance and shall not be shown on plans.
	\|-		\|-
	\|<font color = "grass">(c)</font color = "grass">\|\|~~These dimensions are based on a 17-inch bottom flange~~, ~~revise accordingly for other widths~~. \|\|		\|width="15"\| \|\|<font color = "grass">(a)</font color = "grass">\|\|3" minimum to beam steps, 9" minimum to end of beam.\|\|
	\|-		\|-
	\|valign="top~~" rowspan="3~~"\|<font color = "grass">(d)</font color = "grass">\|\|3" minimum ~~for steel girders~~ and ~~beams~~.\|\|		\| \|\|valign="top"\|<font color = "grass">(b)</font color = "grass">\|\|1/2" minimum and 5" maximum. Use beam step if necessary. With a change in girder size, use thicker laminated pads on the tall girder side if necessary.\|\|width="300"\|
	\|-		\|-
	\|5" ~~minimum~~ for ~~prestressed I girders and bulb-tee girders~~.\|\|		\| \|\|<font color = "grass">(c)</font color = "grass">\|\|These dimensions are based on a 17-inch bottom flange, revise accordingly for other widths.
	\|-		\|-
	\|3½" minimum for prestressed NU girders.\|\|		\| \|\|valign="top" rowspan="3"\|<font color = "grass">(d)</font color = "grass">\|\|3" minimum for steel girders and beams.\|\|
			\|-
			\| \|\|5" minimum for prestressed I girders and bulb-tee girders.\|\|
			\|-
			\| \|\|3½" minimum for prestressed NU girders.\|\|
	\|}		\|}

Line 1,437:		Line 1,439:

	The maximum service load reaction for the details shown shall be 90 kips.		The maximum service load reaction for the details shown shall be 90 kips.

	This limit is based on ASTM A709 Grade 36 steel and bolt pattern shown with bolt threads in the shear plane.		This limit is based on ASTM A709 Grade 36 steel and bolt pattern shown with bolt threads in the shear plane.

	Larger service load reactions will require modified details by design.		Larger service load reactions will require modified details by design.

	When determining service limit state load reaction use DC Loading (excluding barrier or railing) and an additional 50 lb/sf construction load.		When determining service limit state load reaction use DC Loading (excluding barrier or railing) and an additional 50 lb/sf construction load.

Smithk: updated links

2022-06-01T16:26:51Z

updated links

← Older revision		Revision as of 11:26, 1 June 2022
Line 363:		Line 363:
	Anchor bolts are used on bearings with sole plates. For bridges that require seismic details only, design anchor bolts for flexure and shear induced from horizontal seismic forces and design for tension due to uplift forces if present. For bridges that require a seismic analysis, design anchor bolts for flexure induced from horizontal seismic forces and separately design for the effects of combined tension and shear.		Anchor bolts are used on bearings with sole plates. For bridges that require seismic details only, design anchor bolts for flexure and shear induced from horizontal seismic forces and design for tension due to uplift forces if present. For bridges that require a seismic analysis, design anchor bolts for flexure induced from horizontal seismic forces and separately design for the effects of combined tension and shear.

	Limit the number of bolts per bearing to four. Concrete Shear blocks shall be used when anchor bolts cannot be designed to resist earthquake loading. For shear blocks details for P/S girder see, [[751.22 Prestressed Concrete I Girders#751.22.3.14 Concrete Shear Blocks\|EPG 751.22.3.14 Concrete Shear Blocks]]. Use similar details for shear blocks for steel girder.		Limit the number of bolts per bearing to four. Concrete Shear blocks shall be used when anchor bolts cannot be designed to resist earthquake loading. For shear blocks details for P/S girder see, [[751.22 Prestressed Concrete I Girders#751.22.3.13 Concrete Shear Blocks\|EPG 751.22.3.13 Concrete Shear Blocks]]. Use similar details for shear blocks for steel girder.

	Bearing details are shown in [[751.11 Bearings#751.11.3 Details\|EPG 751.11.3 Details]] for two 1 ½”, 2” and 2 ½“ diameter anchor bolts. Consult Structural Project Manager before using bolt diameters larger than 2 1/2". Revise bearing details if four anchor bolts are required by design. For larger than 2 ½” diameter anchor bolt revise details in [[751.11 Bearings#751.11.3.5 Anchor Bolts\|EPG 751.11.3.5 Anchor Bolts]], bearing details and anchor bolt notes in [[751.50 Standard Detailing Notes\|EPG 751.50 Standard Detailing Notes]].		Bearing details are shown in [[751.11 Bearings#751.11.3 Details\|EPG 751.11.3 Details]] for two 1 ½”, 2” and 2 ½“ diameter anchor bolts. Consult Structural Project Manager before using bolt diameters larger than 2 1/2". Revise bearing details if four anchor bolts are required by design. For larger than 2 ½” diameter anchor bolt revise details in [[751.11 Bearings#751.11.3.5 Anchor Bolts\|EPG 751.11.3.5 Anchor Bolts]], bearing details and anchor bolt notes in [[751.50 Standard Detailing Notes\|EPG 751.50 Standard Detailing Notes]].
Line 1,402:		Line 1,402:
	Chairs shall also be used for prestressed girders and beams at fixed intermediate bents where minimum dead load or slope requirements cannot be met by elastomeric laminated fixed bearings and under the smaller girder where girder sizes change.		Chairs shall also be used for prestressed girders and beams at fixed intermediate bents where minimum dead load or slope requirements cannot be met by elastomeric laminated fixed bearings and under the smaller girder where girder sizes change.

	The following detail is not required on the plan sheets but illustrates the location of the bearing with respect to the 7-inch plate. See [[751.22 Prestressed Concrete I Girders#751.22.3.7.4 ~~Reinforcement~~ Details ~~for Bulb-Tee Girders (Type 7 and 8) Using Expansion Intermediate Bent with Continuous Slab~~\|EPG 751.22.3.7.4]] for how chairs are shown on the plan of beam.		The following detail is not required on the plan sheets but illustrates the location of the bearing with respect to the 7-inch plate. See [[751.22 Prestressed Concrete I Girders#751.22.3.7.4 Bent Details\|EPG 751.22.3.7.4]] for how chairs are shown on the plan of beam.
	<center>		<center>
	[[image:751.11.3.6 general.jpg\|center\|500px]]		[[image:751.11.3.6 general.jpg\|center\|500px]]
Line 1,448:		Line 1,448:
	</center>		</center>

	The gap and length of plate is variable and dependent on what is required for rebar placement. The details of the ends of closed concrete intermediate diaphragms will need to be modified from the details shown in [[751.22 Prestressed Concrete I Girders#751.22.3.7 Open Intermediate ~~Bent~~ Diaphragms\|EPG 751.22.3.7 Open Intermediate ~~Bent~~ Diaphragms]].		The gap and length of plate is variable and dependent on what is required for rebar placement. The details of the ends of closed concrete intermediate diaphragms will need to be modified from the details shown in [[751.22 Prestressed Concrete I Girders#751.22.3.8 Open Concrete Intermediate Diaphragms\|EPG 751.22.3.8 Open Concrete Intermediate Diaphragms]].

	[[Category:751 LRFD Bridge Design Guidelines]]		[[Category:751 LRFD Bridge Design Guidelines]]

Smithk: /* 751.11.3.6 Girder/Beam Chairs */ Per BR, updated guidance for concrete diaphragms on bridges

2022-05-31T17:20:06Z

751.11.3.6 Girder/Beam Chairs: Per BR, updated guidance for concrete diaphragms on bridges

← Older revision		Revision as of 12:20, 31 May 2022
Line 1,397:		Line 1,397:
	====751.11.3.6 Girder/Beam Chairs====		====751.11.3.6 Girder/Beam Chairs====

	~~Chairs shall be used at integral bents for prestressed and steel girders and beams if slope requirements cannot be met by elastomeric laminated fixed bearings.~~		'''General'''

	Chairs shall also be used for prestressed girders and beams at fixed intermediate bents where minimum dead load or slope requirements cannot be met by elastomeric laminated fixed bearings and under the smaller girder where girder sizes change.		Chairs shall be used at integral bents for prestressed and steel girders and beams if slope requirements cannot be met by elastomeric laminated fixed bearings.
			Chairs shall also be used for prestressed girders and beams at fixed intermediate bents where minimum dead load or slope requirements cannot be met by elastomeric laminated fixed bearings and under the smaller girder where girder sizes change.

			The following detail is not required on the plan sheets but illustrates the location of the bearing with respect to the 7-inch plate. See [[751.22 Prestressed Concrete I Girders#751.22.3.7.4 Reinforcement Details for Bulb-Tee Girders (Type 7 and 8) Using Expansion Intermediate Bent with Continuous Slab\|EPG 751.22.3.7.4]] for how chairs are shown on the plan of beam.
			<center>
			[[image:751.11.3.6 general.jpg\|center\|500px]]
			'''PLAN OF CHAIR (Skewed bent)'''
			</center>

	~~P/S I-girder shown, steel structures are similar.~~		'''Chair Details'''

	{\| style="margin: 1em auto 1em auto"		The following details shall be provided on the appropriate bent plan sheets. The beams steps and the construction key are shown to illustrate minimum distances, but these items are not required in these details on the plan sheets. Prestressed I girder shown, all other girders and beams are similar.
			<center>
			[[image:751.11.3.6 girder.jpg\|center\|900px]]
			'''GIRDER CHAIR DETAILS'''
			</center>

			:'''Detailing Guidance:'''
			:See EPG 751.50 ([[751.50 Standard Detailing Notes#A4a3. Miscellaneous\|Notes A4a3.1]] and [[751.50 Standard Detailing Notes#(G1.16)\|G1.16 thru G1.19]]) for appropriate notes to be placed with details.
			:<font color = "grass">Green</font color = "grass"> items are guidance and shall not be shown on plans.
			::{\| style="margin: 1em auto 1em auto" align="left"
			\|-
			\|<font color = "grass">(a)</font color = "grass">\|\|3" minimum to beam steps, 9" minimum to end of beam.\|\|
	\|-		\|-
	\|~~rowspan~~="3"\|~~[[Image:751.11.3.6 front elevation 2017.jpg\|600px]]\|\|width~~="~~160~~"\|(a) ~~3 in. minimum when using beam step.~~<br/>~~(b)~~ 1 ~~in.~~ minimum and 5 ~~in.~~ maximum. Use beam step if necessary.		\|valign="top"\|<font color = "grass">(b)</font color = "grass">\|\|1/2" minimum and 5" maximum. Use beam step if necessary. With a change in girder size, use thicker laminated pads on the tall girder side if necessary.\|\|width="300"\|
	\|-		\|-
	\|~~align~~="~~center~~"\|		\|<font color = "grass">(c)</font color = "grass">\|\|These dimensions are based on a 17-inch bottom flange, revise accordingly for other widths. \|\|
	~~{\| border~~="1" ~~cellpadding="3" cellspacing="1" style:"text~~-~~align:center"~~
	\|-		\|-
	\|~~align~~="~~center~~"\|~~'''Maximum Service~~<br/>~~Limit State Load Reaction'''~~		\|valign="top" rowspan="3"\|<font color = "grass">(d)</font color = "grass">\|\|3" minimum for steel girders and beams.\|\|
	\|-		\|-
	\|~~align="center~~"\|~~90 kips~~		\|5" minimum for prestressed I girders and bulb-tee girders.\|\|
	\|}
	\|-		\|-
	\|~~align="center" width="140~~"\|~~Based on details shown, ASTM A709 Grade 36 steel and bolt threads in the shear plane. Larger service load reactions will require modified details by design.~~		\|3½" minimum for prestressed NU girders.\|\|
	\|}		\|}

			'''Maximum Service Limit State Load Reaction'''

	~~[[Image:751~~.11.3.~~6 beam chair~~.~~jpg\|550px\|center]]~~		The maximum service load reaction for the details shown shall be 90 kips.
			This limit is based on ASTM A709 Grade 36 steel and bolt pattern shown with bolt threads in the shear plane.
			Larger service load reactions will require modified details by design.
			When determining service limit state load reaction use DC Loading (excluding barrier or railing) and an additional 50 lb/sf construction load.

	~~[[Image:751.11.3.6 side May 17 2017.jpg\|450px\|center]]~~		'''Possible Variations to Aid in Rebar Placement'''

	:~~::Instructions:~~		The following variations of the above details shall be discussed with the Structural Project Manager or Structural Liaison Engineer if required to reduce conflict between the vertical angels and the beam reinforcement.
	~~::::When determining service limit state load reaction use DC Loading (excluding barrier or railing) and an additional 50 lb~~/~~sf construction load.~~		<center>
			[[image:751.11.3.6 variations.jpg\|750px]]
			</center>

	~~::::See EPG 751~~.~~50 (~~[~~https://epg~~.~~modot.org/index.php?title=~~751.~~50_Standard_Detailing_Notes#A4a3~~.~~_Miscellaneous Notes A4a3~~.~~1] and [[~~751.~~50 Standard Detailing Notes#(G1.16)\|G1~~.~~16 thru G1~~.19]]~~) for appropriate notes to be placed with details~~.		The gap and length of plate is variable and dependent on what is required for rebar placement. The details of the ends of closed concrete intermediate diaphragms will need to be modified from the details shown in [[751.22 Prestressed Concrete I Girders#751.22.3.7 Open Intermediate Bent Diaphragms\|EPG 751.22.3.7 Open Intermediate Bent Diaphragms]].

	[[Category:751 LRFD Bridge Design Guidelines]]		[[Category:751 LRFD Bridge Design Guidelines]]