Tie Bars | Tie Bar Installation Problems | Tie Bar Spacing |Tie Bar Design

                            

Tie Bars | Tie Bar Installation Problems | Tie Bar Spacing |Tie Bar Design  

INTRODUCTION :

Tie Bars:

 Tie Bars are deformed steel bars, deformed epoxy coated steels, or connectors that are used to hold faces of rigid slabs in contact, as per AASHTO, 1993. Not only are they used to decline transverse cracking but also avoid separation and differential deflection of lanes.

Moreover, tie bars are not designed to act as a load transfer device and not advised to be employed as a load transfer means, but they might offer some minimal amount of load transfer. Additionally, they need to be protected from corrosion.

Lastly, they are commonly utilized at longitudinal joints or between an edge joint and a curb or shoulder. Typically, tie bars are 12.5mm or 16mm in diameter and between 0.6 and 1.0 m long.

 

Tie Bar Installation Problems:

1. Bars are missing.
2. Poorly adjusted equipment.
3. Concrete around bars is poorly consolidated.
4. Too stiff mix, often caused by mix delays.
5. Tie bar misplacement

 

Tie Bar Spacing:

 

Table 1 and Table 2 are used to determine spacing of tie bars for bar diameter of 12.5mm and 16mm, respectively.

Table 1 Spacing of Tie bars for Steel Yield Strength of 280MPa and Bar Diameter of 12.5mm

Concrete Thickness, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm
-	3000	3600	4800	7200
225	650	550	400	275
250	600	500	400	250
275	550	450	350	225
300	500	400	325	225

Table 2 Spacing of Tie bars for Steel Yield Strength of 280MPa and Bar Diameter of 16mm

Concrete Thickness, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm	Distance to Free Edge, mm
-	3000	3600	4800	7200
225	1050	875	650	425
250	950	775	600	400
275	850	725	525	350
300	775	650	500	325

Advantages

1. Tie bars improve the performance of pavement joints substantially.
2. They increase the initial cost but reduce life cycle cos

 Tie Bar Design:

 

Area of steel per unit length of joint is obtained by equating the total friction to the total tension developed in the tie bars

a_ts A_s = B M y_c †                                                       

Length of embedment required to develop a bond strength equal to working stress of steel

Lt                                                                                                                      d ats

    

a_ts A_s = 2 P a_bc                         or                L_t = 2 abc                             

σ_ts        Allowable tensile stress in steel = 1400 kg/cm² A_s            Area of tie bar

B         distance b/w the joint and nearest free edge h       Slab thickness

γ_c         Unit weight of concrete

f          Coefficient of subgrade restraint (max 1.5) L_t        Length of tie bar

P         Perimeter of tie bar

d          Diameter of tie bar

σ_bc        Allowable bond stress in concrete     = 24.6 kg/cm² for deformed tie bars

= 17.5 kg/cm² for plain tie bars

 

Details of Tie Bars for Longitudinal Joint of Two-Lane Rigid Pavements

Slab Thickness cm	Tie bar details, cm
	Diameter mm	Max. spacing, cm		Minimum Length, cm
		Plain bars	Deformed bars	Plain bars	Deformed bars
15	8	33	53	44	48
	10	52	83	51	56
20	10	39	62	51	56
	12	56	90	58	64
25	12	45	72	58	64
	16	80	128	72	80
30	12	37	60	58	64
	16	66	106	72	80
35	12	32	51	57	64
	16	57	91	72	80

Note: The recommended details are based on the following values of design parameters σ_ts Allowable tensile stress in steel                                       =   2000 kg/cm² for deformed bars

=    1250 kg/cm² for plain bars

 

σ_bc           Allowable bond stress in concrete  =    24.6 kg/cm2 for deformed bars

=    17.5 kg/cm² for plain bars

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