Hydraulic and earth engineering – Fluid control – treatment – or containment – Flow control
Reexamination Certificate
1998-06-16
2003-07-22
Hartmann, Gary (Department: 3673)
Hydraulic and earth engineering
Fluid control, treatment, or containment
Flow control
C405S288000
Reexamination Certificate
active
06595722
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to concrete reinforced corrugated metal plate arch-type structures, such as used in overpass bridges, water conduits, or underpasses, capable of supporting large superimposed loads under shallow covers such as heavy vehicular traffic and more particularly a structure which may be substituted for standard concrete or steel beam structures.
BACKGROUND OF THE INVENTION
Over the years, corrugated metal sheets or plates have proved themselves to be a durable, economical and versatile engineering material. Flexible arch-type structures made from corrugated metal plates have played an important part in the construction of culverts, storm sewers, subdrains, spillways, underpasses, conveyor conduits and service tunnels; for highways, railways, airports, municipalities, recreation areas, industrial parks, flood and conservation projects, water pollution abatement and many other programmes.
One of the main design challenges in respect of buried corrugated metal arch-type structure is that a relatively thin metal shell is required to resist relatively large loading around its perimeter such as lateral earth pressures, groundwater pressure, overburden pressure as well as other live and/or dead load over the structure. The capacity of such a structure in resisting perimeter loading is, apart from being a function of the strength of the surrounding soil, directly related to the corrugation profile and the thickness of the shell. While evenly distributed perimeter loads, such as earth and water pressures, generally would not create instability in an installed structure, the structure is more susceptible to uneven or localized loading conditions such as uneven earth pressure distribution during backfilling or live loads on the installed structure due to vehicular traffic. Uneven earth pressure distribution during the backfilling of the arch structure causes the structure to distort or peak, rendering the shape of the finished structure different from its intended most structurally sound shape. Live loads over the top of the structure, on the other hand, creates a localized loading condition which could cause failure in the roof portion of the structure.
A localized vertical load such as a live vehicular load imposed over an arch-type structure will create both bending stresses and axial stresses in the structure. Bending stresses are caused by the downward deformation of the roof thereby generating positive bending moments in the crown portion of the structure and negative bending moments near the hip portions of the structure. Axial stresses are compressive stresses caused by a component of the live load acting along the transverse cross-sectional fibre of the arch structure. In a buried metal arch structure design, the ratio of the bending stress to the axial stress experienced under a specific vertical load varies according to the thickness of the overburden. The thicker the overburden, the more distributed the vertical load becomes when it reaches the arch structure and the less bending the structure will be subjected to. The stress in an arch structure under a thick overburden is therefore primarily axial stress.
Corrugated metal sheets tend to fail more easily under bending than under axial compression. Conventional corrugated metal arch-type design deals with bending stresses created by live loads by increasing the overburden thickness, thereby disbursing the localized live loads over the thickness of the overburden and over a larger surface on the arch, the bending stresses on the arch is therefore minimized and the majority of the load is converted into axial forces. However, it is obvious that, by increasing the overburden thickness, the earth pressure on the structure is increased and stronger metal plates are therefore required. The need for a thick overburden also creates severe design limitations, such as limitation on the size of the clearance envelope under the structure or the angle of approach of a roadway over the structure. In a situation where the overburden thickness is limited and is shallow, the live load problem is traditionally solved by positioning an elongated stress relieving slab, usually made of reinforced concrete, near or immediately below the roadway extending above the area of shallow backfill. The elongated slab will act as a load spreading device so that localized vehicular loads will be distributed over a larger area on the metal arch surface. The problem with a stress relieving slab is that it requires on site fabrication thus involving additional fabrication time and substantial costs in labour and material. Moreover, in areas where concrete is not available, this is not a viable option.
Attempts have been made to strengthen a corrugated metal arch structure by the use of reinforcing ribs. In U.S. Pat. No. 4,141,666, reinforcing members are used on the outside of a box culvert to increase its load carrying capacity. The problem with that invention is that sections of the structure between the reinforcing ribs are considerably weaker than at the reinforcing ribs and hence, when loaded, there is a differential deflection or undulating effect along the length of the structure. To reduce this problem, longitudinal members are secured to the inside of the culvert to reduce undulation, particularly along the crown and base portions. It is apparent, however, that when these structures are used over stream beds or the like, it is not desirable to include inside the structure any attachments because of their tendency of being destroyed by ice flows and floods.
In U.S. Pat. No. 4,318,635, multiple arch-shape reinforcing ribs are applied to the interior/exterior of culverts to provide for reinforcement in the sides, crown and intermediate haunch or hip portions. Although such spaced apart reinforcing ribs enhance the strength of the structure to resist loads, they do not overcome the undulation problem in the structure and can add unnecessary weight to the structure by way of superfluous reinforcement. In addition to the above disadvantages, reinforcing ribs in this type of structure are often time consuming and complicated to install adversely affecting the costs of construction. Moreover, where relatively widely spaced rib stiffeners are used, structural design analyses become difficult for these structures. The discontinuity of the reinforcement and hence the variation in stiffness along the longitudinal length of a structure makes it difficult to develop the full plastic moment capacity of the section, thereby giving rise to a design that is generally unnecessarily conservative and uneconomical.
U.S. Pat. No. 3,508,406 by Fisher discloses a composite arch structure having a flexible corrugated metal shell with longitudinally extending concrete buttresses on either side of the structure. It is specifically taught that in the case of a wide spanning arch structure, the concrete buttresses may be connected with additional stiffening members extending over the top portion of the structure. Similarly, in U.S. Pat. No. 4,390,306 by the same inventor, an arch structure is taught wherein a stiffening and load distributing member is structurally fixed to the crown portion of the arch extending longitudinally for the majority of the length of the structure. It is also provided that the composite arch structure should preferably include longitudinally extending, load spreading buttresses on either side of the arch structure. The top longitudinal extending stiffener and buttresses can be made of concrete or metal and may even consist of sections of corrugated plate having its ridges extending in the length direction of the culvert.
In the Fisher patents, continuous reinforcement is provided along the structure by means of the crown stiffener and the buttresses. The buttresses are designed to provide stability to the flexible structure during the installation stage, that is, before the structure is being entirely buried and supported by the backfill. They provide lengths of consolidated material at locations to resist distortio
AIL International Inc.
Barnes & Thornburg
Hartmann Gary
LandOfFree
Composite concrete metal encased stiffeners for metal plate... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composite concrete metal encased stiffeners for metal plate..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composite concrete metal encased stiffeners for metal plate... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3062796