Courtesy of the Porto Biomechanics Laboratory, Three-dimensional MoCap systems are used worldwide on a daily basis. Underwater cameras are used for swimming analysis. Data stations are in charge of reconstructing the position of each marker and tracking their trajectory in real time.įigure 10.5. Some cameras, namely those from Qualisys, can also incorporate several other interesting features such as high-speed and high-resolution video, electromagnetic shielding for use in MRI rooms, and waterproofing for underwater acquisition ( Fig. 10.5).
Nowadays, high-speed marker tracking is possible, up to around 1000 frames per second (fps) with full field of view (FOV) or up to 10,000 fps with reduced FOV. A camera is outfitted with a special strobe infrared light, which is reflected back to the camera by the subject's markers and used to calculate the markers' coordinates through in-camera processing software. These markers are usually made of polystyrene hemispheres covered in special retroreflective tape (with glass beads). The most accurate systems use lightweight, small-dimension (from 2.5 to 50 mm), passive retroreflective markers or clusters that are placed on the subject's body in accordance with a predefined anthropometric model. These cameras are used to capture the two-dimensional coordinates of special markers from different views ( Fig. 10.4). The key hardware components of MoCap optical systems are the motion cameras. Therefore the difference τ ~ aG = τ aG − τ aG g is bounded. The actual ground reaction torque is also bounded because of its cyclic nature and the finite body weight. ( 24) are modeled by passive mechanical components and finite penetration, and d aX and d aZ are functions of the bounded kinematic references. ( 23) is bounded because F X and F Z in Eq. The distances d aX and d aZ depend on the gait-based references θ _ r g, temporal gait parameters, and the contact profiles assumed for the prosthetic feet. These parameters can be obtained from experiments similar to those reported in. P (m/s) is the horizontal velocity of the contact point with respect to the ground, and sgn (.) is the sign function.PEN (m/s) are the penetration and penetration rate of the foot into the ground, k - (N/m) and e - are the spring coefficient and spring exponent, c - d (N s/m) is the damping coefficient, μ - is the friction coefficient, x.4.10 or its equivalent for the hogging region for an unplated beam.
Furthermore and to stress and reiterate a point, they can also be used for determining the shear load at the datum point to cause crack sliding in an unplated beam or slab (V dat) u by simply substituting P plate = 0 in Eq. 4.12 acts prior to cracking and that is why it is included in the shear load to cause cracking in Eqs 4.18 and 4.19.Įquations 4.24 and 4.25 can be used for metal and FRP plates, in fact plates of any material. In contrast, the active prestressing force F ps in Fig. Hence, the passive prestress P plate does not affect the shear load to cause cracking (V dat) cr-Plate as it simply does not exist prior to cracking. It needs to be emphasised that the passive prestress induced by the plate P plate does not act before an intermediate diagonal crack has formed as it is induced by the aggregate interlock sliding action across the crack. 4.9 has been adapted as follows to include a passive prestress term.Ĥ.25 ( ( V d a t ) u − p r e s ) h o g = 0.4 ( f 1 ( f c ) f 2 ( h ) f 3 ( ρ ) f 4 ( σ p s f c ) p l a t e ) f c b c h ( 1 + ( x h ) 2 − x h ) 1 + K W
A coefficient of 4 was found to correlate well with test data and also with prestressed code approaches described in Section 4.5.2. 4.9 gives a conservative estimate of the increase in the shear to cause CDC debonding. A comparison of this increase in the shear capacity with tests in which critical diagonal cracks were known to occur ( Oehlers et al 2004a) showed that the coefficient 2 in Eq. 4.9 for unplated beams is increased to F ps+P plate. In which case, the prestress force term F ps in the prestress function of Eq.
DERIC JOHN OEHLERS, RUDOLF SERACINO, in Design of FRP and Steel Plated RC Structures, 2004 4.4.1.4 Shear to cause crack sliding in tension face plated sections – passive prestress approachĪn alternative to converting the maximum plate force P plate into an equivalent area of longitudinal reinforcement, as in Section 4.4.1.3, is to assume that the maximum plate force P plate directly applies a passive prestress across the diagonal crack as explained in Section 4.2.1 and in Figs 4.2 and 4.3.