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HOBAS PIPE USA

Technical Advice Sheet HOBAS Tee Base Manhole System General: The HOBAS tee base manhole system consists of a HOBAS tee base and a riser system. The riser system can consist of a one-piece fiberglass riser, segmented fiberglass riser, or segmented RCP riser. The tee base consists of a HOBAS thru-pipe (or fitting) and a HOBAS vertical stub, connected at the saddle-cut with a structural fiberglass lamination. The main pipe can be straight (no angle) or mitered to a specific angle (typically up to 90º). The structural fiberglass lamination is very strong and will typically equal or exceed the tensile strength of the pipe itself. Although the pipe can withstand up to 5% long-term uniform deflection, the irregularly shaped saddle connection can tolerate very little deformation. The tee base must therefore be prevented from distorting. This is typically done with a concrete encasement (sometimes needs reinforcement). Details regarding necessary reinforcement will depend on conditions and will need to be designed by a structural concrete design engineer.


Encasement: Traditionally, the body of the tee base is encased, with the encasement stopping before the joint on each end (see FIGURE 1). While this will effectively protect the tee base, it creates a dramatically different support condition for the pipes on each side of the coupling at each of the adjacent joints. The tee base thru-pipe will be held perfectly round, supported rigidly, and the adjacent pipe will be supported elastically by the native soil and the pipe-zone surround system. While the FWC coupling that seals this joint is flexible and quite forgiving, it cannot easily maintain seal when connecting pipes with dramatically different shapes. This phenomenon is magnified as the main diameter increases. Experience indicates that with sizes 48” and larger (typically), it is advisable to extend the concrete encasement past the joint (1’ – 3’ depending on diameter – see FIGURE 2). This will eliminate the risk of leak due to differential deflection of the coupling joints on each side of the tee base.

This will, however, create a rigid connection in the pipe wall, posing another, albeit smaller, potential risk. If the bedding and side support in the elastically supported pipe immediately adjacent to the encasement is not adequate, the resulting stress in the pipe wall where the encasement ends could be sufficient to damage the pipe wall. Excellent bedding and side support at this transition is critical. While this transition area is important and has associated risks, cases of pipe wall damage at rigid concrete connections are rare.


Conclusion: For tee bases with thru-pipes of 48” and larger, HOBAS’ experience indicates extending the concrete encasement past the joints by about 1’ – 3’ (depending on diameter) is advisable. Excellent bedding and side support is critical in the elastically supported pipe adjacent to the end of the encasement.

Rigid Connections

Rigid connections of pipes (such as to structures, to manholes or at the ends of encasements) create additional installation challenges to achieve buried success. The new issues caused by connections such as these include shearing at the interface, beam bending of the pipe, over rotation of joints, excessive joint pullout (draw) and differing support conditions across joint locations. It is frequently a common practice to incorporate a joint (or two joints) immediately adjacent to the “rigid” connection to minimize the effects of potential differential settlement between the manhole or structure (or encasement) and the attached (connected) pipe(s). At first thought, this appears to be a sound engineering approach. While this practice does aid in safely accommodating differential settlements (shearing) and minimizing of pipe beam bending, it increases the risk of excessive joint angular deflection, unacceptable joint draw and differential pipe deflection across joints with different support conditions (i.e. pipe on one side rigidly supported (concrete encased – likely zero deflection) and pipe on the opposite side elastically supported (soil and backfill – likely 2% +/- deflection)). The last item (differential pipe deflection across a joint), when of sufficient magnitude (typically over 0.5”), can result in joint leakage and / or damage. Therefore, in many instances (particularly larger diameters and deep covers), the installation may be most successful by locating the first joint away from the rigid connection by a distance of at least 2 or 3 pipe diameters. Doing this will likely create a very similar pipe support condition across all joints, which usually results in nearly equal pipe deflections on both sides of the joint, thereby maximizing the joint performance. This procedure will, however, create a cantilever configuration for the first pipe exiting the rigid connection and does little to aid potential differential settlements. Having a cantilevered pipe also increases the risk of excessive pipe beam bending and shear at the interface, however, these potential risks can be greatly minimized by adequate bedding beneath the pipe to provide proper longitudinal support. Regardless of joint proximity to rigid connections, a successful installation must achieve similar pipe deflections across joints and avoid significant differential settlements. Joints may be located anywhere when these items are well controlled. In our experience, it is generally easier to achieve good, uniform longitudinal support than to control buried deflections to very small amounts. Therefore, for larger diameters (>36” to 42” typically), we have found it’s best to locate joints away from the rigid connection interface. For smaller diameters (<24” to 30”), one may be most successful having a joint(s) in close proximity to the rigid connection interface.

Elevation View

Plan View

0-Miter Tee-Base

Sample Drawings fo Tee-BasesTrinity River Authority (TRA)Arlington, TX

GAC

(Typical)

03-09-2016

HOBAS

Project: PART NO.:

CONTRACTOR:

DRWN. BY REV

Description:

Notes:1. Concrete Encasement (designed by others) is to resist all T‐Base deformations.

2. Contractor to coordinate top Elevation of Concrete Encasement with FRP Manhole Manufacturer.

3. See HOBAS Tee Base Manhole System Technical Advise Sheets for additional information.

4. See next pages for recommended tee‐base dimensions.

15 in (Typ.)

Base DNØ

Neck DNØ

L

1 - 3 ft Encasement Past Coupling

FWC Coupling

Plain End(bevel typical)


Elevation View

Plan View

1-Miter Tee-Base


GAC

(Typical)

03-09-2016

HOBAS

Project: PART NO.:

CONTRACTOR:

DRWN. BY REV

Description:





15 in (Typ.)

Base DNØ

Neck DNØ




0° - 30°

L/2

L/2

18'' see notes 18'' 60'' 18'' 60'' 18'' 60''

20'' see notes 18'' 60'' 18'' 60'' 20'' 60''

24'' see notes 18'' 60'' 24'' 60'' 24'' 60''

27'' see notes 24'' 60'' 24'' 60'' 27'' 60''

28'' see notes 24'' 60'' 27'' 60'' 28'' 60''

30'' ~8''‐10'' 24'' 60'' 27'' 60'' 30'' 60''

33'' ~8''‐11'' 24'' 60'' 30'' 60'' 33'' 60''

36'' ~9''‐12'' 24'' 60'' 30'' 60'' 36'' 78''

41'' ~10''‐14'' 24'' 60'' 30'' 60'' 36'' 78''

42'' ~11''‐14'' 24'' 60'' 30'' 60'' 36'' 78''

44'' ~11''‐15'' 24'' 60'' 30'' 60'' 36'' 78''

45'' ~11''‐15'' 24'' 60'' 30'' 60'' 36'' 78''

48'' ~12''‐16'' 24'' 78'' 36'' 78'' 48'' 108''

51'' ~13''‐17'' 24'' 78'' 36'' 78'' 48'' 108''

54'' ~14''‐18'' 24'' 78'' 36'' 78'' 48'' 108''

57'' ~14''‐19'' 24'' 78'' 36'' 78'' 48'' 108''

60'' ~15''‐20'' 36'' 78'' 48'' 108'' 60'' 108''

63'' ~16''‐21'' 36'' 78'' 48'' 108'' 60'' 108''

66'' ~17''‐22'' 36'' 78'' 48'' 108'' 60'' 108''

69'' ~17''‐23'' 36'' 78'' 48'' 108'' 60'' 108''

72'' ~18''‐24'' 36'' 78'' 48'' 108'' 60'' 108''

78'' ~20''‐26'' 36'' 78'' 48'' 108'' 60'' 108''

84'' ~21''‐28'' 36'' 108'' 48'' 108'' 60'' 108''

85'' ~21''‐29'' 36'' 108'' 48'' 108'' 60'' 108''

90'' ~23''‐30'' 36'' 108'' 48'' 108'' 60'' 108''

96'' ~24''‐32'' 48'' 108'' 60'' 108'' 72'' 117''

104'' ~26''‐35'' 48'' 108'' 60'' 108'' 72'' 117''

110'' ~28''‐37'' 48'' 108'' 60'' 108'' 72'' 117''

120'' ~30''‐40'' 48'' 108'' 60'' 108'' 72'' 117''

126'' ~32''‐42'' 48'' 108'' 60'' 108'' 72'' 117''

Notes:

1.Dimensions shown are typical to optimize construction costs. Tee‐bases can have different

neck & radius, as well as different operating conditions that may affect the overall length.

2. Length of encasement past coupling recommended for pipe diameters greater than 30".

Please contact Hobas for project specific recommendations for diameters smaller than 30".

Typical Tee‐Base Dimensions

0 & 1‐Miter Teebase

Neck DNøTotal

Length 'L'Neck DNø

Total

Length 'L'Neck DNø

Total

Length 'L'

Base

DNø

Approximate

Length of

Encasement

past joint

Elevation View

Plan View

2-Miter Tee-Base


GAC

(Typical)

03-09-2016

HOBAS

Project: PART NO.:

CONTRACTOR:

DRWN. BY REV

Description:







Neck DNØ

Radius

Leg

Leng

th

Leg Length

30° - 60°

Base DNØ

1 - 3 ft EncasementPast Coupling

Elevation View

Plan View

3-Miter Tee-Base


GAC

(Typical)

03-09-2016

HOBAS

Project: PART NO.:

CONTRACTOR:

DRWN. BY REV

Description:







Leg Length

Neck DNØ

Radius60° - 90°

Leg

Leng

th


Base DNØ

Neck

DNø

Leg

Length

Neck

DNø

Leg

Length

Neck

DNø

Leg

Length

Neck

DNø

Leg

Length60°‐75° 75°‐90°

18'' 27'' see notes ‐ 25'' 18'' 25'' ‐ 30'' 18'' 30'' 35'' 40''

20'' 30'' see notes ‐ 26'' 20'' 26'' ‐ 31'' 20'' 31'' 37'' 42''

24'' 36'' see notes 24'' 28'' 24'' 28'' 24'' 33'' 24'' 33'' 41'' 48''

27'' 38'' see notes 24'' 29'' 27'' 29'' 24'' 34'' 27'' 34'' 42'' 50''

28'' 40'' see notes 24'' 30'' 28'' 30'' 24'' 35'' 28'' 35'' 44'' 52''

30'' 42'' ~8''‐10'' 24'' 31'' 30'' 31'' 24'' 36'' 30'' 36'' 45'' 54''

33'' 44'' ~8''‐11'' 24'' 32'' 33'' 32'' 24'' 37'' 33'' 37'' 47'' 56''

36'' 48'' ~9''‐12'' 24'' 33'' 36'' 35'' 24'' 39'' 36'' 39'' 50'' 60''

41'' 52'' ~10''‐14'' 36'' 36'' 41'' 38'' 36'' 42'' 41'' 42'' 53'' 64''

42'' 54'' ~11''‐14'' 36'' 37'' 42'' 38'' 36'' 43'' 42'' 43'' 55'' 66''

44'' 55'' ~11''‐15'' 36'' 37'' 44'' 39'' 36'' 44'' 44'' 44'' 56'' 67''

45'' 57'' ~11''‐15'' 36'' 38'' 45'' 40'' 36'' 45'' 45'' 45'' 57'' 69''

48'' 60'' ~12''‐16'' 36'' 39'' 48'' 42'' 36'' 46'' 48'' 46'' 59'' 72''

51'' 63'' ~13''‐17'' 48'' 40'' 51'' 43'' 48'' 48'' 51'' 48'' 62'' 75''

54'' 66'' ~14''‐18'' 48'' 41'' 54'' 46'' 48'' 49'' 54'' 49'' 64'' 78''

57'' 68'' ~14''‐19'' 48'' 42'' 57'' 48'' 48'' 50'' 57'' 52'' 66'' 81''

60'' 70'' ~15''‐20'' 48'' 43'' 60'' 50'' 48'' 51'' 60'' 53'' 68'' 84''

63'' 73'' ~16''‐21'' 60'' 44'' 63'' 52'' 60'' 53'' 63'' 55'' 70'' 87''

66'' 75'' ~17''‐22'' 60'' 45'' 66'' 53'' 60'' 54'' 66'' 57'' 72'' 90''

69'' 78'' ~17''‐23'' 60'' 47'' 69'' 55'' 60'' 55'' 69'' 59'' 74'' 93''

72'' 80'' ~18''‐24'' 60'' 48'' 72'' 56'' 60'' 56'' 72'' 60'' 76'' 96''

78'' 84'' ~20''‐26'' 60'' 51'' 78'' 61'' 60'' 60'' 78'' 65'' 81'' 102''

84'' 88'' ~21''‐28'' 60'' 53'' 84'' 64'' 60'' 63'' 84'' 68'' 85'' 106''

85'' 90'' ~21''‐29'' 60'' 54'' 85'' 65'' 60'' 64'' 85'' 70'' 86'' 108''

90'' 95'' ~23''‐30'' 60'' 57'' 90'' 68'' 60'' 68'' 90'' 73'' 91'' 114''

96'' 100'' ~24''‐32'' 60'' 60'' 96'' 72'' 60'' 72'' 96'' 77'' 96'' 120''

104'' 108'' ~26''‐35'' 60'' 63'' 104'' 78'' 60'' 76'' 104'' 83'' 101'' 126''

110'' 112'' ~28''‐37'' 60'' 66'' 110'' 81'' 60'' 80'' 110'' 86'' 106'' 132''

120'' 120'' ~30''‐40'' 60'' 72'' 120'' 88'' 60'' 88'' 120'' 94'' 116'' 144''

126'' 126'' ~32''‐42'' 60'' 72'' 126'' 95'' 60'' 88'' 126'' 100'' 116'' 144''

Notes:

1.Dimensions shown are typical to optimize construction costs. Tee‐bases can have different

neck & radius, as well as different operating conditions that may affect the overall length.

2. Length of encasement past coupling recommended for pipe diameters greater than 30".

Please contact Hobas for project specific recommendations for diameters smaller than 30".

Typical Tee‐Base Dimensions

3‐Miter

Leg LengthRadius

45°‐60°

2‐Miter Tee‐Base

30°‐45°Base

DNø

Approximate

Length of

Encasement

past joint

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