EP1132534A2

EP1132534A2 - Moment-resisting beam to column connection

Info

Publication number: EP1132534A2
Application number: EP01105947A
Authority: EP
Inventors: Ersin Arioglu
Original assignee: Yapi Merkezi Prefabrikasyon AS
Current assignee: Yapi Merkezi Prefabrikasyon AS
Priority date: 2000-03-09
Filing date: 2001-03-09
Publication date: 2001-09-12
Also published as: EP1132534A3

Abstract

A method of connecting a pre-cast horizontal building element (beam) (3) to a pre-cast vertical building element (column) (2) by post-tensioning after one end (4) of the said beam (3) leans laterally on one side face (5) of the said column, and as a result of obtaining a connection (1) which is capable of transferring moment of flexion and shear force whereby the connection exhibits reliable and sufficient strength for resistance against seismic loads. Post-tensioning the beam (3) to the column (2) is performed by the tensioning and locking of the post-tensioning tendons (8) which are fed in the tendon sleeves (7) that are embedded in the column (2).

Description

I. THE SUBJECT MATTER OF THE INVENTION:

The invention concerns a post-tensioning moment-resisting beam to column connection method for connecting pre-cast concrete beam and column members that will exhibit reliable and sufficient strength under high seismic environmental factors. With this invention, the connection of the beam to the column is realized by employing post-tensioning after the pre-cast beam is positioned to lean against a face of the column, whereby a connection capable of transferring moment of flexion, shear force and axial loads is obtained which exhibits reliable and sufficient strength for resistance against seismic loads.

II. STATE OF THE ART:

Pre-cast and pre-stressed concrete building elements have found widespread use in the field of construction engineering within the last 25 to 30 years.
Within this framework, variety of pre-cast pre-stressed concrete building elements are being widely used both as the main frame of the buildings and as other architectural elements in the construction of wide variety of buildings such as industrial buildings, commercial buildings, high-rise housings, motels, schools, recreational buildings and bridges.
The major advantages of this method of construction method stem from the ability to prefabricate the building elements in special production facilities prior to being sent to the construction site, and further from the fact that it is pre-stressed and finally from the fact that it is made of concrete.
Pre-casting enables significant time savings in the construction time periods. Properly programmed work schedule will enable carrying out a number of applications simultaneously. For example, concurrently while carrying out land survey, layout work, ground breaking and construction of the foundation, it is also possible to pre-cast the other superstructure members simultaneously at a different location. Furthermore, the erection of the pre-cast members does take much shorter period of time in comparison working with cast-in-place concrete. The production of the superstructure members in a manufacturing plant facilitates a much better quality control and makes possible the achievement of higher standardization which in turn enables obtaining of a high quality of concrete with much higher resistance properties. This type of production besides having the time saving advantage, also increases productivity and therefore leads to cost savings in the materials used. Furthermore, the ability of undertaking production in closed manufacturing facilities, which is not effected from environmental and weather conditions, enables the use of curing techniques which considerably shorten the time of production. Since high degree of standardization can be achieved in pre-casting, it is possible to produce building elements with predetermined precise geometrical proportions.
Compared with the normal reinforced concrete, prestressing enables the production of building elements having longer spans with shallower depths by using less material. Pre-cast pre-stressed concrete element thus produced, shall be much lighter than the ordinary reinforced concrete required for the same span, and therefore, easier to manipulate and more economical to haul. Furthermore, pre-cast pre-stressed concrete has the added advantage over the ordinary reinforced concrete with respect to more controllable performance in terms of cracking and deflection. Though it is possible to produce the building elements as ordinary reinforced concrete instead of as pre-stressed elements, because of its clear advantages the pre-stressed concrete is preferred in practice practically in all cases over ordinary reinforced concrete where pre-casting is involved.
Finally, as it is well known, a chief advantage using concrete as a construction material over other materials such as wood and steel stem from its quality of resistance to fire, its durability and its requirement of very little maintenance.
Counter to the many technical advantages cited above of using pre-cast pre-stressed building elements in constructing a building, the major disadvantage relates to the comparative weakness which is exhibited in the connection of the building elements to each other.
In real world conditions the structural frame system formed of a number of pre-cast elements has to withstand a variety of stresses and movements imposed by forces and load factors such as gravity loads, repeated loads, creep and shrinkage forces, changes in the temperature and finally the intermittent lateral forces of the wind and earthquake. Accordingly, the connections of the pre-cast building elements should have the properties enabling them to withstand these stresses and movements.
Therefore, the subject of developing appropriate and satisfactory connections for pre-cast concrete elements has been has been an area of study since the emergence of the production of pre-cast building elements. The search in this area still continues in the world.
In the early days, trial and error methods or complex empirical expressions which did not directly related to imposed shears, moments, direct forces and force transmission performances naturally did not yield satisfactory results. The concept of "shear-friction" developed later in time has been of significant help in the development of rational design methods that would replace the empirically designed connections. However, the problem of finding connections that will transmit the required forces without unduly restraining the volume chance movements is still an area of importance.
Since the behavior of a connection during cyclic loading can be different than for static loading and since that the behavior of the connections will influence the structural repose and the loads induced into the structure, present day studies have concerned themselves with various design principles of various connection types and thereof to the designing of connection types which incorporate the moment, shear force and normal force transmitting characteristics.
Whether it is a single story or a multi-story construction, the main frame of a building is formed of vertical (column) and horizontal (beam) building elements. These building elements each of which are pre-cast separately at another location are connected to each other to form the main frame of the building. Beam-column connections according to their load transfer characteristics can be classified as rigid, as semi-rigid, or as simply supported. Rigid connections are utilized in frame structures to provide resistance against vertical and lateral loads. And these connections are capable of transmitting shear, moment and axial loads.
During an earthquake whether they are of single or multi-story in all kinds of buildings the connections are subjected to monotonic gravity loads and lateral loads. As a consequence the Turkish Earthquake Zone Building Code require that the connections be of rigid type capable of transmitting shear, moment and lateral loads.
These rigid beam-column connections are classified into two main groups namely of "dry connections" and "wet connections".
Dry connections are types of connections employed to connect vertical (column) and horizontal (beam) building elements into which steel elements such as profiles, bolts, extrusions, etc. are embedded during the pre-casting of the building elements. The said steel elements are embedded into the appropriate places of the pre-cast members at spots where the building elements are to be connected together. The connection is realized by generally welding or bolting a third element into the embedded steel articles. In this type of connections the elements to be joined together are manufactured according to prescribed sizes and shapes, and cast-in-place concrete is not employed in the connection procedure.
The building elements to be joined by wet connection method are manufactured with a certain gap at the portion of the pre-cast building element where the connection will occur so that cast-in-place cement can be employed to realize the connection. To form the connection between the pre-cast members the reinforcement cage designed at the joint is filled with fresh cement.
Both of these two types of connections in actual performance exhibit the following disadvantages:
In dry connections, the welding together of the steel connecting elements is a very critical process requiring sensitive quality control procedures.
Achievement of this type of quality control is very important since employing adequate quality control to ensure a quality weld at the construction site is a rather difficult process. In cases where transmitting of high magnitude loads are necessary, the anchorage of steel connecting elements does create problems with respect to the accumulation of tensions on the beam and on the region of the connection.
In wet connections the problem arises with respect to proper coherence (between the pre-cast concrete and fresh concrete at the joint) of the concrete employed and cast at different time periods. And also it is rather difficult to achieve sufficient adherence length. Furthermore, the enlarging of the area where the fresh concrete is employed does lead to new complications.
The subject matter of this invention as explained herewith is a rigid connection method which is different from the connection methods that were explained above. The connection method of this invention involve a mechanism which exhibits a good performance in the transfer of the moment load, shear forces and normal forces as well as the cyclic or alternating loads such as those earthquake induced.

IV. DESCRIPTION OF THE DRAWINGS:

Figure 1, is a front sectional view of the post-tensioning beam to column connection.
Figure 2, is a perspective view of the post-tensioning beam to column connection.

IV. DESCRIPTION OF THE INVENTION:

The invention concerns a method of connecting a pre-cast horizontal building element (beam) (3) to a pre-cast vertical building element (column) (2) by post-tensioning, after one end (4) of the said horizontal building element (beam) (3) leans laterally on one side face (5) of the said vertical building element (column), and as a result, of obtaining a connection (1) which is capable of transferring moment of flexion and shear force whereby the connection exhibits reliable and sufficient strength for resistance against seismic loads.
After the said one end (4) of the horizontal building element (beam) (3) is leaned on one side face (5) of the said vertical building element (column) (2), post-tensioning the beam (3) to the column (2) is realized by the tensioning and locking of the post-tensioning tendons (8) which are fed in the tendon sleeves (7) that are embedded in the vertical building element (column) (2) running parallel with the axis of the longitudinal direction of the horizontal element (beam) (3). Post-tensioning is realized by tensioning the post-tensioning tendons (8) running inside the tendon sleeves (7) and locking the ends of the tendons (post-tensioning) at the anchorage pockets.
In this type of connection, when connecting the beam (3) to the column (2), the beam or the beams (3) may be placed at one side only or at both sides respectively of the vertical building element (column)(2). And accordingly the post-tensioning of the tendon is employed at one end of the tendon or at both ends.
In this type of connection the building elements are pre-cast in the predetermined dimensions as required by their final use. However, the number of the post-tensioning tendons (8) and their position in the cross section of the beam are determined according to the static calculations of the static magnitudes to be transmitted. Both the tendon sleeves (8) which are suitable sized with the diameter of the tendon (8) and the post-tensioning anchorage heads are cast into the building element (beam) during the casting of the pre-cast element. The tendons are positioned by taking into consideration that during an earthquake the tensioning will occur at the top and the bottom regions of the beam due to characteristics of the seismic loads.
Therefore, with the method provided by this invention, a post-tensioning connection capable of transmitting moment and shear force is obtained with the use of high resistance tendons without the need for bearing pads and without adherence.

Claims

A post-tensioning connection (1) method for connecting a pre-cast horizontal building element (beam) (3) to a pre-cast vertical building element (column) (2), characterized in that in their final positions after the connection one end (4) of the said horizontal building element (beam) (3) leans laterally on one side face (5) of the said vertical building element (column) (2).
A post-tensioning beam to column connection method as claimed in Claim 1, characterized in that after the said one end (4) of the horizontal building element (beam) (3) is leaned on one side face (5) of the said vertical building element (column) (2), post-tensioning the beam (3) to the column (2) is performed by the tensioning and locking of the post-tensioning tendons (8) which are fed in the tendon sleeves (7) that are embedded in the vertical building element (column) (2) running parallel with the axis of the longitudinal direction of the horizontal element (beam) (3).
A post-tensioning beam to column connection method as claimed in Claim 1, characterized in that post-tensioning is performed by tensioning the post-tensioning tendons (8) running inside the tendon sleeves (7) and locking both ends of the tendons (8) (post-tensioning) at the anchorage pockets.
A post-tensioning beam to column connection method as claimed in Claims 1 to 3, characterized in that when connecting the beam (3) to the column (2), the beam or the beams (3) may be placed leaning at one side face only or leaning at the faces of both sides respectively of the vertical building element (column) (2).
A post-tensioning beam to column connection method as claimed in Claims 1 to 3, characterized in that the post-tensioning of the tendon is performed at one end of the tendon.